Method and device for transmitting discovery reference signal in wireless access system supporting unlicensed band

ABSTRACT

The present invention relates to a wireless access system supporting an unlicensed band, methods for configuring a discovery reference signal (DRS), methods for re-configuring subframes for same, methods for transmitting a DRS, and devices for supporting same. A method for a base station transmitting a discovery reference signal (DRS), according to one embodiment of the present invention, comprises: a step of configuring a DRS transmitted from an unlicensed band cell (Ucell) configured in an unlicensed band; and transmitting the configured DRS during a DRS opportunity, wherein the DRS includes a primary synchronization signal (PSS), a secondary synchronization signal (SSS), and a cell-specific reference signal (CRS), wherein the SSS is generated on the basis of a subframe (SF) number of a subframe in which the DRS opportunity has occurred, wherein the SSS is generated on the basis of a sequence corresponding to SF number 0 when the SF number is between SF numbers 0 to 4, and the SSS is generated on the basis of a sequence corresponding to SF number 5 when the SF number is between SF numbers 5 to 9.

TECHNICAL FIELD

The present disclosure relates to a wireless access system supporting anunlicensed band, and more particularly, to methods for configuring aDiscovery Reference Signal (DRS), methods for reconfiguring subframesfor the same, methods for transmitting a DRS, and apparatuses supportingthe same.

BACKGROUND ART

Wireless access systems have been widely deployed to provide varioustypes of communication services such as voice or data. In general, awireless access system is a multiple access system that supportscommunication of multiple users by sharing available system resources (abandwidth, transmission power, etc.) among them. For example, multipleaccess systems include a Code Division Multiple Access (CDMA) system, aFrequency Division Multiple Access (FDMA) system, a Time DivisionMultiple Access (TDMA) system, an Orthogonal Frequency Division MultipleAccess (OFDMA) system, and a Single Carrier Frequency Division MultipleAccess (SC-FDMA) system.

DISCLOSURE Technical Problem

An aspect of the present disclosure is to provide a method fortransmitting and receiving data efficiently in a wireless access systemsupporting an unlicensed band.

Another aspect of the present disclosure is to provide methods forconfiguring and transmitting a Discovery Reference Signal (DRS) in aLicensed Assisted Access (LAA) system.

Another aspect of the present disclosure is to provide methods forreconfiguring subframe numbers for an Unlicensed Cell (UCell) togenerate signals included in a DRS in an LAA system.

Another aspect of the present disclosure is to provide informationindicating a time when a DRS occasion occurs in an LAA system.

Another aspect of the present disclosure is to provide apparatusessupporting the above methods.

It will be appreciated by persons skilled in the art that the objectsthat could be achieved with the present disclosure are not limited towhat has been particularly described hereinabove and the above and otherobjects that the present disclosure could achieve will be more clearlyunderstood from the following detailed description.

Technical Solution

The present disclosure relates to a wireless access system supporting anunlicensed band, and provides methods for configuring a DiscoveryReference Signal (DRS), methods for reconfiguring subframes for thesame, methods for transmitting a DRS, and apparatuses supporting thesame.

In an aspect of the present disclosure, a method for transmitting a DRSby a base station in a wireless access system supporting an unlicensedband includes configuring the DRS to be transmitted in an unlicensedband cell (UCell) configured in the unlicensed band, and transmittingthe configured DRS in a DRS occasion. The DRS may include a primarysynchronization signal (PSS), a secondary synchronization signal (SSS),and a cell-specific reference signal (CRS), and the SSS may be generatedbased on a subframe (SF) number of an SF in which the DRS occasionoccurs. If the SF number is SF #0 to SF #4, the SSS may be generatedbased on a sequence corresponding to SF #0, and if the SF number is SF#5 to SF #9, the SSS may be generated based on a sequence correspondingto SF #5.

The method may further include performing a channel sensing procedure todetermine whether the UCell is idle, before transmitting the DRS.

In another aspect of the present disclosure, a base station fortransmitting a DRS in a wireless access system supporting an unlicensedband includes a transmitter, and a processor for configuring the DRS.The processor may be configured to configure the DRS to be transmittedin an unlicensed band cell (UCell) configured in the unlicensed band,and to transmit the configured DRS in a DRS occasion by controlling thetransmitter. The DRS may include a PSS, an SSS, and a CRS, and the SSSmay be generated based on a subframe (SF) number of an SF in which theDRS occasion occurs. If the SF number is SF #0 to SF #4, the SSS may begenerated based on a sequence corresponding to SF #0, and if the SFnumber is SF #5 to SF #9, the SSS may be generated based on a sequencecorresponding to SF #5.

The processor may be configured further to perform a channel sensingprocedure to determine whether the UCell is idle, before transmittingthe DRS.

In the above aspects, if the SF number of an SF carrying the CRS is SF#0 to SF #4, the CRS may be generated based on the sequencecorresponding to SF #0, and if the SF number of the SF carrying the CRSis SF #5 to SF #9, the CRS may be generated based on the sequencecorresponding to SF #5.

The DRS may be transmitted along with a physical downlink shared channel(PDSCH) only in SF #0 or SF #5.

The DRS may be configured to further include a channel statusinformation-reference signal (CSI-RS).

It is to be understood that both the foregoing general description andthe following detailed description of the present disclosure areexemplary and explanatory and are intended to provide furtherexplanation of the disclosure as claimed.

Advantageous Effects

The embodiments of the present disclosure have the following effects.

First, data may be transmitted and received efficiently in a wirelessaccess system supporting an unlicensed band.

Secondly, a Discovery Reference Signal (DRS) may be configured andtransmitted adaptively according to the characteristics of acontention-based Licensed Assisted Access (LAA) system.

Thirdly, a DRS used in a licensed band of a legacy system may beutilized in an LAA system by reconfiguring subframes in an UnlicensedCell (UCell) of the LAA system.

Fourthly, the probability of dropping a DRS in a DRS occasion by a UserEquipment (UE) may be reduced by explicitly or implicitly indicating tothe UE a time when the DRS occasion occurs.

It will be appreciated by persons skilled in the art that the effectsthat can be achieved with the present disclosure are not limited to whathas been particularly described hereinabove and other advantages of thepresent disclosure will be more clearly understood from the followingdetailed description taken in conjunction with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the disclosure and are incorporated in and constitute apart of this application, illustrate embodiments of the disclosure andtogether with the description serve to explain the principle of thedisclosure. In the drawings:

FIG. 1 is a view illustrating physical channels and a signaltransmission method using the physical channels;

FIG. 2 is a view illustrating exemplary radio frame structures;

FIG. 3 is a view illustrating an exemplary resource grid for theduration of a downlink slot;

FIG. 4 is a view illustrating an exemplary structure of an uplinksubframe;

FIG. 5 is a view illustrating an exemplary structure of a downlinksubframe;

FIG. 6 is a view illustrating Physical Uplink Control Channel (PUCCH)formats 1a and 1b in a normal Cyclic Prefix (CP) case, and FIG. 7 is aview illustrating PUCCH formats 1a and 1b in an extended CP case;

FIG. 8 is a view illustrating PUCCH format 2/2a/2b in the normal CPcase, and

FIG. 9 is a view illustrating PUCCH format 2/2a/2b in the extended CPcase;

FIG. 10 is a view illustrating Acknowledgment/Negative Acknowledgment(ACK/NACK) channelization for PUCCH formats 1a an 1b;

FIG. 11 is a view illustrating channelization for a hybrid structure ofPUCCH format 1 a/1b and PUCCH format 2/2a/2b in the same PhysicalResource Block (PRB);

FIG. 12 is a view illustrating a PRB allocation method;

FIG. 13 is a view illustrating exemplary Component Carriers (CCs) andexemplary Carrier Aggregation (CA) in a Long Term Evolution-Advanced(LTE-A) system, which are used in embodiments of the present disclosure;

FIG. 14 is a view illustrating a subframe structure based oncross-carrier scheduling in the LTE-A system, which is used inembodiments of the present disclosure;

FIG. 15 is a view illustrating an exemplary configuration of servingcells according to cross-carrier scheduling used in embodiments of thepresent disclosure;

FIG. 16 is a view illustrating an exemplary new PUCCH format based onblock spreading;

FIG. 17 is a view illustrating an exemplary configuration of a ResourceUnit (RB) with time-frequency units;

FIG. 18 is a view illustrating an exemplary method for resourceallocation and retransmission in asynchronous Hybrid Automatic RepeatreQuest (HARQ);

FIG. 19 is a conceptual view illustrating a Coordinated Multi-Point(CoMP) system operating in a CA environment;

FIG. 20 is a view illustrating an exemplary subframe to which UserEquipment (UE)-specific Reference Signals (RSs) (UE-RSs) are allocated,which may be used in embodiments of the present disclosure;

FIG. 21 is a view illustrating an exemplary multiplexing of a legacyPhysical Downlink Channel (PDCCH), a Physical Downlink Shared Channel(PDSCH), and an Enhanced PDCCH (E-PDCCH) in the LTE/LTE-A system;

FIG. 22 is a view illustrating an exemplary CA environment supported inan LTE-Unlicensed (LTE-U) system;

FIG. 23 is a view illustrating an exemplary Frame Based Equipment (FBE)operation as one of Listen-Before-Talk (LBT) operations;

FIG. 24 is a block diagram illustrating the FBE operation;

FIG. 25 is a view illustrating an exemplary Load Based Equipment (LBE)operation as one of the LBT operations;

FIG. 26 is a view illustrating methods for transmitting a DiscoveryReference Signal (DRS) supported in a Licensed Assisted Access (LAA)system;

FIG. 27 is a view illustrating a Channel Access Procedure (CAP) andContention Window Adjustment (CWA);

FIG. 28 is a view illustrating a method for transmitting a DRS in theLAA system;

FIG. 29 is a view illustrating an exemplary DRS transmission pattern;

FIG. 30 is a view illustrating DRS transmission patterns which may beapplied to the LAA system;

FIG. 31 is another view illustrating DRS transmission patterns which maybe applied to the LAA system;

FIG. 32 is another view illustrating DRS transmission patterns which maybe applied to the LAA system;

FIG. 33 is a view illustrating a method for configuring a DRStransmission pattern irrespective of Cell-specific Reference Signal(CRS) positions, which may be applied to the LAA system;

FIG. 34 is a view illustrating methods for configuring subframe numbersfor DRS transmission, which may be applied to the LAA system;

FIG. 35 is a view illustrating an exemplary DRS transmission methodwhich may be applied to the LAA system; and

FIG. 36 is a block diagram of apparatuses for implementing the methodsdescribed with reference to FIGS. 1 to 35.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention as described below in detail relateto a wireless access system supporting an unlicensed band, and providemethods for configuring a Discovery Reference Signal (DRS), methods forre-configuring subframes for the same, methods for transmitting a DRS,and an apparatus supporting the same.

The embodiments of the present disclosure described below arecombinations of elements and features of the present disclosure inspecific forms. The elements or features may be considered selectiveunless otherwise mentioned. Each element or feature may be practicedwithout being combined with other elements or features. Further, anembodiment of the present disclosure may be constructed by combiningparts of the elements and/or features. Operation orders described inembodiments of the present disclosure may be rearranged. Someconstructions or elements of any one embodiment may be included inanother embodiment and may be replaced with corresponding constructionsor features of another embodiment.

In the description of the attached drawings, a detailed description ofknown procedures or steps of the present disclosure will be avoided lestit should obscure the subject matter of the present disclosure. Inaddition, procedures or steps that could be understood to those skilledin the art will not be described either.

Throughout the specification, when a certain portion “includes” or“comprises” a certain component, this indicates that other componentsare not excluded and may be further included unless otherwise noted. Theterms “unit”, “-or/er” and “module” described in the specificationindicate a unit for processing at least one function or operation, whichmay be implemented by hardware, software or a combination thereof. Inaddition, the terms “a or an”, “one”, “the” etc. may include a singularrepresentation and a plural representation in the context of the presentdisclosure (more particularly, in the context of the following claims)unless indicated otherwise in the specification or unless contextclearly indicates otherwise.

In the embodiments of the present disclosure, a description is mainlymade of a data transmission and reception relationship between a BaseStation (BS) and a User Equipment (UE). A BS refers to a terminal nodeof a network, which directly communicates with a UE. A specificoperation described as being performed by the BS may be performed by anupper node of the BS.

Namely, it is apparent that, in a network comprised of a plurality ofnetwork nodes including a BS, various operations performed forcommunication with a UE may be performed by the BS, or network nodesother than the BS. The term ‘BS’ may be replaced with a fixed station, aNode B, an evolved Node B (eNode B or eNB), an Advanced Base Station(ABS), an access point, etc.

In the embodiments of the present disclosure, the term terminal may bereplaced with a UE, a Mobile Station (MS), a Subscriber Station (SS), aMobile Subscriber Station (MSS), a mobile terminal, an Advanced MobileStation (AMS), etc.

A transmission end is a fixed and/or mobile node that provides a dataservice or a voice service and a reception end is a fixed and/or mobilenode that receives a data service or a voice service. Therefore, a UEmay serve as a transmission end and a BS may serve as a reception end,on an UpLink (UL). Likewise, the UE may serve as a reception end and theBS may serve as a transmission end, on a DownLink (DL).

The embodiments of the present disclosure may be supported by standardspecifications disclosed for at least one of wireless access systemsincluding an Institute of Electrical and Electronics Engineers (IEEE)802.xx system, a 3rd Generation Partnership Project (3GPP) system, a3GPP Long Term Evolution (LTE) system, and a 3GPP2 system. Inparticular, the embodiments of the present disclosure may be supportedby the standard specifications, 3GPP TS 36.211, 3GPP TS 36.212, 3GPP TS36.213, 3GPP TS 36.321 and 3GPP TS 36.331. That is, the steps or parts,which are not described to clearly reveal the technical idea of thepresent disclosure, in the embodiments of the present disclosure may beexplained by the above standard specifications. All terms used in theembodiments of the present disclosure may be explained by the standardspecifications.

Reference will now be made in detail to the embodiments of the presentdisclosure with reference to the accompanying drawings. The detaileddescription, which will be given below with reference to theaccompanying drawings, is intended to explain exemplary embodiments ofthe present disclosure, rather than to show the only embodiments thatcan be implemented according to the disclosure.

The following detailed description includes specific terms in order toprovide a thorough understanding of the present disclosure. However, itwill be apparent to those skilled in the art that the specific terms maybe replaced with other terms without departing the technical feature andscope of the present disclosure.

For example, the term Transmission Opportunity Period (TxOP) isinterchangeable with transmission period, Transmission (Tx) burst, orReserved Resource Period (RRP). Further, a Listen Before Talk (LBT)operation may be performed for the same purpose as that of carriersensing for determining whether a channel is in an idle state, ClearChannel Assessment (CCA), and a Channel Access Procedure (CAP).

Hereinafter, 3GPP LTE/LTE-A systems are explained, which are examples ofwireless access systems.

The embodiments of the present disclosure can be applied to variouswireless access systems such as Code Division Multiple Access (CDMA),Frequency Division Multiple Access (FDMA), Time Division Multiple Access(TDMA), Orthogonal Frequency Division Multiple Access (OFDMA), SingleCarrier Frequency Division Multiple Access (SC-FDMA), etc.

CDMA may be implemented as a radio technology such as UniversalTerrestrial Radio Access (UTRA) or CDMA2000. TDMA may be implemented asa radio technology such as Global System for Mobile communications(GSM)/General packet Radio Service (GPRS)/Enhanced Data Rates for GSMEvolution (EDGE). OFDMA may be implemented as a radio technology such asIEEE 802.11 (WiFi), IEEE 802.16 (WiMAX), IEEE 802.20, Evolved UTRA(E-UTRA), etc.

UTRA is a part of Universal Mobile Telecommunications System (UMTS).3GPP LTE is a part of Evolved UMTS (E-UMTS) using E-UTRA, adopting OFDMAfor DL and SC-FDMA for UL. LTE-Advanced (LTE-A) is an evolution of 3GPPLTE. While the embodiments of the present disclosure are described inthe context of a 3GPP LTE/LTE-A system in order to clarify the technicalfeatures of the present disclosure, the present disclosure is alsoapplicable to an IEEE 802.16e/m system, etc.

1. 3GPP LTE/LTE-A System

In a wireless access system, a UE receives information from an eNB on aDL and transmits information to the eNB on a UL. The informationtransmitted and received between the UE and the eNB includes generaldata information and various types of control information. There aremany physical channels according to the types/usages of informationtransmitted and received between the eNB and the UE.

1.1 System Overview

FIG. 1 illustrates physical channels and a general signal transmissionmethod using the physical channels, which may be used in embodiments ofthe present disclosure.

When a UE is powered on or enters a new cell, the UE performs initialcell search (S11). The initial cell search involves acquisition ofsynchronization to an eNB. Specifically, the UE synchronizes its timingto the eNB and acquires information such as a cell Identifier (ID) byreceiving a Primary Synchronization Channel (P-SCH) and a SecondarySynchronization Channel (S-SCH) from the eNB.

Then the UE may acquire information broadcast in the cell by receiving aPhysical Broadcast Channel (PBCH) from the eNB.

During the initial cell search, the UE may monitor a DL channel state byreceiving a Downlink Reference Signal (DL RS).

After the initial cell search, the UE may acquire more detailed systeminformation by receiving a Physical Downlink Control Channel (PDCCH) andreceiving a Physical Downlink Shared Channel (PDSCH) based oninformation of the PDCCH (S12).

To complete connection to the eNB, the UE may perform a random accessprocedure with the eNB (S13 to S16). In the random access procedure, theUE may transmit a preamble on a Physical Random Access Channel (PRACH)(S13) and may receive a PDCCH and a PDSCH associated with the PDCCH(S14). In the case of contention-based random access, the UE mayadditionally perform a contention resolution procedure includingtransmission of an additional PRACH (S15) and reception of a PDCCHsignal and a PDSCH signal corresponding to the PDCCH signal (S16).

After the above procedure, the UE may receive a PDCCH and/or a PDSCHfrom the eNB (S17) and transmit a Physical Uplink Shared Channel (PUSCH)and/or a Physical Uplink Control Channel (PUCCH) to the eNB (S18), in ageneral UL/DL signal transmission procedure.

Control information that the UE transmits to the eNB is genericallycalled Uplink Control Information (UCI). The UCI includes a HybridAutomatic Repeat and reQuest Acknowledgement/Negative Acknowledgement(HARQ-ACK/NACK), a Scheduling Request (SR), a Channel Quality Indicator(CQI), a Precoding Matrix Index (PMI), a Rank Indicator (RI), etc.

In the LTE system, UCI is generally transmitted on a PUCCH periodically.However, if control information and traffic data should be transmittedsimultaneously, the control information and traffic data may betransmitted on a PUSCH. In addition, the UCI may be transmittedaperiodically on the PUSCH, upon receipt of a request/command from anetwork.

FIG. 2 illustrates exemplary radio frame structures used in embodimentsof the present disclosure.

FIG. 2(a) illustrates frame structure type 1. Frame structure type 1 isapplicable to both a full Frequency Division Duplex (FDD) system and ahalf FDD system.

One radio frame is 10 ms (Tf=307200·Ts) long, including equal-sized 20slots indexed from 0 to 19. Each slot is 0.5 ms (Tslot=15360·Ts) long.One subframe includes two successive slots. An ith subframe includes2ith and (2i+1)th slots. That is, a radio frame includes 10 subframes. Atime required for transmitting one subframe is defined as a TransmissionTime Interval (TTI). Ts is a sampling time given as Ts=1/(15kHz×2048)=3.2552×10−8 (about 33 ns). One slot includes a plurality ofOrthogonal Frequency Division Multiplexing (OFDM) symbols or SC-FDMAsymbols in the time domain by a plurality of Resource Blocks (RBs) inthe frequency domain.

A slot includes a plurality of OFDM symbols in the time domain. SinceOFDMA is adopted for DL in the 3GPP LTE system, one OFDM symbolrepresents one symbol period. An OFDM symbol may be called an SC-FDMAsymbol or symbol period. An RB is a resource allocation unit including aplurality of contiguous subcarriers in one slot.

In a full FDD system, each of 10 subframes may be used simultaneouslyfor DL transmission and UL transmission during a 10-ms duration. The DLtransmission and the UL transmission are distinguished by frequency. Onthe other hand, a UE cannot perform transmission and receptionsimultaneously in a half FDD system.

The above radio frame structure is purely exemplary. Thus, the number ofsubframes in a radio frame, the number of slots in a subframe, and thenumber of OFDM symbols in a slot may be changed.

FIG. 2(b) illustrates frame structure type 2. Frame structure type 2 isapplied to a Time Division Duplex (TDD) system. One radio frame is 10 ms(Tf=307200·Ts) long, including two half-frames each having a length of 5ms (=153600·Ts) long. Each half-frame includes five subframes each being1 ms (=30720·Ts) long. An ith subframe includes 2ith and (2i+1)th slotseach having a length of 0.5 ms (Tslot=15360·Ts). Ts is a sampling timegiven as Ts=1/(15 kHz×2048)=3.2552×10−8 (about 33 ns).

A type-2 frame includes a special subframe having three fields, DownlinkPilot Time Slot (DwPTS), Guard Period (GP), and Uplink Pilot Time Slot(UpPTS). The DwPTS is used for initial cell search, synchronization, orchannel estimation at a UE, and the UpPTS is used for channel estimationand UL transmission synchronization with a UE at an eNB. The GP is usedto cancel UL interference between a UL and a DL, caused by themulti-path delay of a DL signal.

[Table 1] below lists special subframe configurations (DwPTS/GP/UpPTSlengths).

TABLE 1 Normal cyclic prefix in downlink Extended cyclic prefix indownlink UpPTS UpPTS Special Normal Extended Normal Extended subframecyclic prefix cyclic prefix cyclic prefix cyclic prefix configurationDwPTS in uplink in uplink DwPTS in uplink in uplink 0  6592 · T_(s) 2192· T_(s) 2560 · T_(s)  7680 · T_(s) 2192 · T_(s) 2560 · T_(s) 1 19760 ·T_(s) 20480 · T_(s) 2 21952 · T_(s) 23040 · T_(s) 3 24144 · T_(s) 25600· T_(s) 4 26336 · T_(s)  7680 · T_(s) 4384 · T_(s) 5120 · T_(s) 5  6592· T_(s) 4384 · T_(s) 5120 · T_(s) 20480 · T_(s) 6 19760 · T_(s) 23040 ·T_(s) 7 21952 · T_(s) 12800 · T_(s) 8 24144 · T_(s) — — — 9 13168 ·T_(s) — — —

FIG. 3 illustrates an exemplary structure of a DL resource grid for theduration of one DL slot, which may be used in embodiments of the presentdisclosure.

Referring to FIG. 3, a DL slot includes a plurality of OFDM symbols inthe time domain. One DL slot includes 7 OFDM symbols in the time domainand an RB includes 12 subcarriers in the frequency domain, to which thepresent disclosure is not limited.

Each element of the resource grid is referred to as a Resource Element(RE). An RB includes 12×7 REs. The number of RBs in a DL slot, NDLdepends on a DL transmission bandwidth. A UL slot may have the samestructure as a DL slot.

FIG. 4 illustrates a structure of a UL subframe which may be used inembodiments of the present disclosure.

Referring to FIG. 4, a UL subframe may be divided into a control regionand a data region in the frequency domain. A PUCCH carrying UCI isallocated to the control region and a PUSCH carrying user data isallocated to the data region. To maintain a single carrier property, aUE does not transmit a PUCCH and a PUSCH simultaneously. A pair of RBsin a subframe are allocated to a PUCCH for a UE. The RBs of the RB pairoccupy different subcarriers in two slots. Thus it is said that the RBpair frequency-hops over a slot boundary.

FIG. 5 illustrates a structure of a DL subframe that may be used inembodiments of the present disclosure.

Referring to FIG. 5, up to three OFDM symbols of a DL subframe, startingfrom OFDM symbol 0 are used as a control region to which controlchannels are allocated and the other OFDM symbols of the DL subframe areused as a data region to which a PDSCH is allocated. DL control channelsdefined for the 3GPP LTE system include a Physical Control FormatIndicator Channel (PCFICH), a PDCCH, and a Physical Hybrid ARQ IndicatorChannel (PHICH).

The PCFICH is transmitted in the first OFDM symbol of a subframe,carrying information about the number of OFDM symbols used fortransmission of control channels (i.e. the size of the control region)in the subframe. The PHICH is a response channel to a UL transmission,delivering an HARQ ACK/NACK signal. Control information carried on thePDCCH is called Downlink Control Information (DCI). The DCI transportsUL resource assignment information, DL resource assignment information,or UL Transmission (Tx) power control commands for a UE group.

1.2 Physical Downlink Control Channel (PDCCH)

1.2.1 PDCCH Overview

The PDCCH may deliver information about resource allocation and atransport format for a Downlink Shared Channel (DL-SCH) (i.e. a DLgrant), information about resource allocation and a transport format foran Uplink Shared Channel (UL-SCH) (i.e. a UL grant), paging informationof a Paging Channel (PCH), system information on the DL-SCH, informationabout resource allocation for a higher-layer control message such as arandom access response transmitted on the PDSCH, a set of Tx powercontrol commands for individual UEs of a UE group, Voice Over InternetProtocol (VoIP) activation indication information, etc.

A plurality of PDCCHs may be transmitted in the control region. A UE maymonitor a plurality of PDCCHs. A PDCCH is transmitted in an aggregate ofone or more consecutive Control Channel Elements (CCEs). A PDCCH made upof one or more consecutive CCEs may be transmitted in the control regionafter subblock interleaving. A CCE is a logical allocation unit used toprovide a PDCCH at a code rate based on the state of a radio channel. ACCE includes a plurality of RE Groups (REGs). The format of a PDCCH andthe number of available bits for the PDCCH are determined according tothe relationship between the number of CCEs and a code rate provided bythe CCEs.

1.2.2 PDCCH Structure

A plurality of PDCCHs for a plurality of UEs may be multiplexed andtransmitted in the control region. A PDCCH is made up of an aggregate ofone or more consecutive CCEs. A CCE is a unit of 9 REGs each REGincluding 4 REs. Four Quadrature Phase Shift Keying (QPSK) symbols aremapped to each REG. REs occupied by RSs are excluded from REGs. That is,the total number of REGs in an OFDM symbol may be changed depending onthe presence or absence of a cell-specific RS. The concept of an REG towhich four REs are mapped is also applicable to other DL controlchannels (e.g. the PCFICH or the PHICH). Let the number of REGs that arenot allocated to the PCFICH or the PHICH be denoted by NREG. Then thenumber of CCEs available to the system is NCCE (└N_(REG)/9┘) and theCCEs are indexed from 0 to NCCE−1.

To simplify the decoding process of a UE, a PDCCH format including nCCEs may start with a CCE having an index equal to a multiple of n. Thatis, given CCE i, the PDCCH format may start with a CCE satisfying i modn=0.

The eNB may configure a PDCCH with 1, 2, 4, or 8 CCEs. {1, 2, 4, 8} arecalled CCE aggregation levels. The number of CCEs used for transmissionof a PDCCH is determined according to a channel state by the eNB. Forexample, one CCE is sufficient for a PDCCH directed to a UE in a good DLchannel state (a UE near to the eNB). On the other hand, 8 CCEs may berequired for a PDCCH directed to a UE in a poor DL channel state (a UEat a cell edge) in order to ensure sufficient robustness.

[Table 2] below illustrates PDCCH formats. 4 PDCCH formats are supportedaccording to CCE aggregation levels as illustrated in [Table 2].

TABLE 2 PDCCH Number of CCE Number of Number of PDCCH format (n) REGbits 0 1 9 72 1 2 18 144 2 4 36 288 3 8 72 576

A different CCE aggregation level is allocated to each UE because theformat or Modulation and Coding Scheme (MCS) level of controlinformation delivered in a PDCCH for the UE is different. An MCS leveldefines a code rate used for data coding and a modulation order. Anadaptive MCS level is used for link adaptation. In general, three orfour MCS levels may be considered for control channels carrying controlinformation.

Regarding the formats of control information, control informationtransmitted on a PDCCH is called DCI. The configuration of informationin PDCCH payload may be changed depending on the DCI format. The PDCCHpayload is information bits. [Table 3] lists DCI according to DCIformats.

TABLE 3 DCI Format Description Format Resource grants for PUSCHtransmissions (uplink) 0 Format Resource assignments for single codewordPDSCH transmission 1 (transmission modes 1, 2 and 7) Format Compactsignaling of resource assignments for single codeword 1A PDSCH (allmodes) Format Compact resource assignments for PDSCH using rank-1 closed1B loop precoding (mode 6) Format Very compact resource assignments forPDSCH (e.g., 1C paging/broadcast system information) Format Compactresource assignments for PDSCH using multi-user 1D MIMO(mode 5) FormatResource assignments for PDSCH for closed loop MIMO 2 operation (mode 4)Format resource assignments for PDSCH for open loop MIMO operation 2A(mode 3) Format Power control commands for PUCCH and PUSCH with 2-bit/1-3/3A bit power adjustment Format Scheduling of PUSCH in one UL cell withmulti-antenna port 4 transmission mode

Referring to [Table 3], the DCI formats include Format 0 for PUSCHscheduling, Format 1 for single-codeword PDSCH scheduling, Format 1A forcompact single-codeword PDSCH scheduling, Format 1C for very compactDL-SCH scheduling, Format 2 for PDSCH scheduling in a closed-loopspatial multiplexing mode, Format 2A for PDSCH scheduling in anopen-loop spatial multiplexing mode, and Format 3/3A for transmission ofTransmission Power Control (TPC) commands for uplink channels. DCIFormat 1A is available for PDSCH scheduling irrespective of thetransmission mode of a UE.

The length of PDCCH payload may vary with DCI formats. In addition, thetype and length of PDCCH payload may be changed depending on compact ornon-compact scheduling or the transmission mode of a UE.

The transmission mode of a UE may be configured for DL data reception ona PDSCH at the UE. For example, DL data carried on a PDSCH includesscheduled data, a paging message, a random access response, broadcastinformation on a BCCH, etc. for a UE. The DL data of the PDSCH isrelated to a DCI format signaled through a PDCCH. The transmission modemay be configured semi-statically for the UE by higher-layer signaling(e.g. Radio Resource Control (RRC) signaling). The transmission mode maybe classified as single antenna transmission or multi-antennatransmission.

A transmission mode is configured for a UE semi-statically byhigher-layer signaling. For example, multi-antenna transmission schememay include transmit diversity, open-loop or closed-loop spatialmultiplexing, Multi-User Multiple Input Multiple Output (MU-MIMO), orbeamforming. Transmit diversity increases transmission reliability bytransmitting the same data through multiple Tx antennas. Spatialmultiplexing enables high-speed data transmission without increasing asystem bandwidth by simultaneously transmitting different data throughmultiple Tx antennas. Beamforming is a technique of increasing theSignal to Interference plus Noise Ratio (SINR) of a signal by weightingmultiple antennas according to channel states.

A DCI format for a UE depends on the transmission mode of the UE. The UEhas a reference DCI format monitored according to the transmission modeconfigure for the UE. The following 10 transmission modes are availableto UEs:

(1) Transmission mode 1: Single antenna port (port 0);

(2) Transmission mode 2: Transmit diversity;

(3) Transmission mode 3: Open-loop spatial multiplexing when the numberof layer is larger than 1 or Transmit diversity when the rank is 1;

(4) Transmission mode 4: Closed-loop spatial multiplexing;

(5) Transmission mode 5: MU-MIMO;

(6) Transmission mode 6: Closed-loop rank-1 precoding;

(7) Transmission mode 7: Precoding supporting a single layertransmission, which is not based on a codebook (Rel-8);

(8) Transmission mode 8: Precoding supporting up to two layers, whichare not based on a codebook (Rel-9);

(9) Transmission mode 9: Precoding supporting up to eight layers, whichare not based on a codebook (Rel-10); and

(10) Transmission mode 10: Precoding supporting up to eight layers,which are not based on a codebook, used for CoMP (Rel-11).

1.2.3 PDCCH Transmission

The eNB determines a PDCCH format according to DCI that will betransmitted to the UE and adds a Cyclic Redundancy Check (CRC) to thecontrol information. The CRC is masked by a unique Identifier (ID) (e.g.a Radio Network Temporary Identifier (RNTI)) according to the owner orusage of the PDCCH. If the PDCCH is destined for a specific UE, the CRCmay be masked by a unique ID (e.g. a cell-RNTI (C-RNTI)) of the UE. Ifthe PDCCH carries a paging message, the CRC of the PDCCH may be maskedby a paging indicator ID (e.g. a Paging-RNTI (P-RNTI)). If the PDCCHcarries system information, particularly, a System Information Block(SIB), its CRC may be masked by a system information ID (e.g. a SystemInformation RNTI (SI-RNTI)). To indicate that the PDCCH carries a randomaccess response to a random access preamble transmitted by a UE, its CRCmay be masked by a Random Access-RNTI (RA-RNTI).

Then, the eNB generates coded data by channel-encoding the CRC-addedcontrol information. The channel coding may be performed at a code ratecorresponding to an MCS level. The eNB rate-matches the coded dataaccording to a CCE aggregation level allocated to a PDCCH format andgenerates modulation symbols by modulating the coded data. Herein, amodulation order corresponding to the MCS level may be used for themodulation. The CCE aggregation level for the modulation symbols of aPDCCH may be one of 1, 2, 4, and 8. Subsequently, the eNB maps themodulation symbols to physical REs (i.e. CCE to RE mapping).

1.2.4 Blind Decoding (BD)

A plurality of PDCCHs may be transmitted in a subframe. That is, thecontrol region of a subframe includes a plurality of CCEs, CCE 0 to CCENCCE,k−1. NCCE,k is the total number of CCEs in the control region of akth subframe. A UE monitors a plurality of PDCCHs in every subframe.This means that the UE attempts to decode each PDCCH according to amonitored PDCCH format.

The eNB does not provide the UE with information about the position of aPDCCH directed to the UE in an allocated control region of a subframe.Without knowledge of the position, CCE aggregation level, or DCI formatof its PDCCH, the UE searches for its PDCCH by monitoring a set of PDCCHcandidates in the subframe in order to receive a control channel fromthe eNB. This is called blind decoding. Blind decoding is the process ofdemasking a CRC part with a UE ID, checking a CRC error, and determiningwhether a corresponding PDCCH is a control channel directed to a UE bythe UE.

The UE monitors a PDCCH in every subframe to receive data transmitted tothe UE in an active mode. In a Discontinuous Reception (DRX) mode, theUE wakes up in a monitoring interval of every DRX cycle and monitors aPDCCH in a subframe corresponding to the monitoring interval. ThePDCCH-monitored subframe is called a non-DRX subframe.

To receive its PDCCH, the UE should blind-decode all CCEs of the controlregion of the non-DRX subframe. Without knowledge of a transmitted PDCCHformat, the UE should decode all PDCCHs with all possible CCEaggregation levels until the UE succeeds in blind-decoding a PDCCH inevery non-DRX subframe. Since the UE does not know the number of CCEsused for its PDCCH, the UE should attempt detection with all possibleCCE aggregation levels until the UE succeeds in blind decoding of aPDCCH.

In the LTE system, the concept of Search Space (SS) is defined for blinddecoding of a UE. An SS is a set of PDCCH candidates that a UE willmonitor. The SS may have a different size for each PDCCH format. Thereare two types of SSs, Common Search Space (CSS) andUE-specific/Dedicated Search Space (USS).

While all UEs may know the size of a CSS, a USS may be configured foreach individual UE. Accordingly, a UE should monitor both a CSS and aUSS to decode a PDCCH. As a consequence, the UE performs up to 44 blinddecodings in one subframe, except for blind decodings based on differentCRC values (e.g., C-RNTI, P-RNTI, SI-RNTI, and RA-RNTI).

In view of the constraints of an SS, the eNB may not secure CCEresources to transmit PDCCHs to all intended UEs in a given subframe.This situation occurs because the remaining resources except forallocated CCEs may not be included in an SS for a specific UE. Tominimize this obstacle that may continue in the next subframe, aUE-specific hopping sequence may apply to the starting position of aUSS.

[Table 4] illustrates the sizes of CSSs and USSs.

TABLE 4 PDCCH Number of CCE Number of Number of Format (n) candidates inCSS candidates in USS 0 1 — 6 1 2 — 6 2 4 4 2 3 8 2 2

To mitigate the load of the UE caused by the number of blind decodingattempts, the UE does not search for all defined DCI formatssimultaneously. Specifically, the UE always searches for DCI Format 0and DCI Format 1A in a USS. Although DCI Format 0 and DCI Format 1A areof the same size, the UE may distinguish the DCI formats by a flag forformat 0/format 1 a differentiation included in a PDCCH. Other DCIformats than DCI Format 0 and DCI Format 1A, such as DCI Format 1, DCIFormat 1B, and DCI Format 2 may be required for the UE.

The UE may search for DCI Format 1A and DCI Format 1C in a CSS. The UEmay also be configured to search for DCI Format 3 or 3A in the CSS.Although DCI Format 3 and DCI Format 3A have the same size as DCI Format0 and DCI Format 1A, the UE may distinguish the DCI formats by a CRCscrambled with an ID other than a UE-specific ID.

An SS S_(k) ^((L)) is a PDCCH candidate set with a CCE aggregation levelLϵ{1,2,4,8}. The CCEs of PDCCH candidate set m in the SS may bedetermined by the following equation.

L·{(Y _(k) +m)mod └N _(CCE,k) /L┘}+i  [Equation 1]

Herein, M^((L)) is the number of PDCCH candidates with CCE aggregationlevel L to be monitored in the SS, m=0, . . . , M^((L))−1, i is theindex of a CCE in each PDCCH candidate, and i=0, . . . , L−1.k=└n_(s)/2┘ where n_(s) is the index of a slot in a radio frame.

As described before, the UE monitors both the USS and the CSS to decodea PDCCH. The CSS supports PDCCHs with CCE aggregation levels {4, 8} andthe USS supports PDCCHs with CCE aggregation levels {1, 2, 4, 8}. [Table5] illustrates PDCCH candidates monitored by a UE.

TABLE 5 Search space S_(k) ^((L)) Number of PDCCH Type Aggregation levelL Size [in CCEs] candidates M^((L)) UE-specific 1 6 6 2 12 6 4 8 2 8 162 Common 4 16 4 8 16 2

Referring to [Equation 1], for two aggregation levels, L=4 and L=8,Y_(k) is set to 0 in the CSS, whereas Y_(k) is defined by [Equation 2]for aggregation level L in the USS.

Y _(k)=(A·Y _(k-1))mod D  [Equation 2]

Herein, Y⁻¹=n_(RNTI)≠0, n_(RNTI) indicating an RNTI value. A=39827 andD=65537.

1.3. PUCCH (Physical Uplink Control Channel)

PUCCH may include the following formats to transmit control information.

(1) Format 1: On-Off keying (OOK) modulation, used for SR (SchedulingRequest)

(2) Format 1 a & 1b: Used for ACK/NACK transmission

-   -   1) Format 1 a: BPSK ACK/NACK for 1 codeword    -   2) Format 1b: QPSK ACK/NACK for 2 codewords

(3) Format 2: QPSK modulation, used for CQI transmission

(4) Format 2a & Format 2b: Used for simultaneous transmission of CQI andACK/NACK

(5) Format 3: Used for multiple ACK/NACK transmission in a carrieraggregation environment

[Table 6] shows a modulation scheme according to PUCCH format and thenumber of bits per subframe. Table 7 shows the number of referencesignals (RS) per slot according to PUCCH format. Table 8 shows SC-FDMAsymbol location of RS (reference signal) according to PUCCH format. InTable 6, PUCCH format 2a and PUCCH format 2b correspond to a case ofnormal cyclic prefix (CP).

TABLE 6 PUCCH format Modulation scheme No. of bits per subframe, Mbit 1N/A N/A 1a BPSK 1 1b QPSK 2 2 QPSK 20 2a QPSK + BPSK 21 2b QPSK + BPSK22 3 QPSK 48

TABLE 7 PUCCH format Normal CP Extended CP 1, 1a, 1b 3 2 2, 3 2 1 2a, 2b2 N/A

TABLE 8 PUCCH SC-FDMA symbol location of RS format Normal CP Extended CP1, 1a, 1b 2, 3, 4 2, 3 2, 3 1, 5 3 2a, 2b 1, 5 N/A

FIG. 6 shows PUCCH formats 1a and 1b in case of a normal cyclic prefix.And, FIG. 7 shows PUCCH formats 1a and 1b in case of an extended cyclicprefix.

According to the PUCCH formats 1 a and 1b, control information of thesame content is repeated in a subframe by slot unit. In each UE,ACK/NACK signal is transmitted on a different resource constructed witha different cyclic shift (CS) (frequency domain code) and an orthogonalcover (OC) or orthogonal cover code (OCC) (time domain spreading code)of CG-CAZAC (computer-generated constant amplitude zero autocorrelation) sequence. For instance, the OC includes Walsh/DFTorthogonal code. If the number of CS and the number of OC are 6 and 3,respectively, total 18 UEs may be multiplexed within the same PRB(physical resource block) with reference to a single antenna. Orthogonalsequences w0, w1, w2 and w3 may be applicable to a random time domain(after FFT modulation) or a random frequency domain (before FFTmodulation).

For persistent scheduling with SR, ACK/NACK resource constructed withCS, OC and PRB (physical resource block) may be allocated to a UEthrough RRC (radio resource control. For non-persistent scheduling withdynamic ACK/NACK, the ACK/NACK resource may be implicitly allocated to aUE using a smallest CCE index of PDCCH corresponding to PDSCH.

Length-4 orthogonal sequence (OC) and length-3 orthogonal sequence forPUCCH format 1/1a/1b are shown in Table 9 and Table 10, respectively.

TABLE 9 Sequence index Orthogonal sequences n_(oc) (n_(s)) [w(0) . . .w(N_(SF) ^(PUCCH) − 1)] 0 [+1 +1 +1 +1] 1 [+1 −1 +1 −1] 2 [+1 −1 −1 +1]

TABLE 10 Sequence index Orthogonal sequences n_(oc) (n_(s)) [w(0) . . .w(N_(SF) ^(PUCCH) − 1)] 0 [1 1 1] 1 [1 e^(j2π/3) e^(j4π/3)] 2 [1e^(j4π/3) e^(j2π/3)]

Orthogonal sequence (OC) [w(0) . . . w(N_(RS) ^(PUCCH)−1)] or areference signal in PUCCH format 1/1a/1b is shown in Table 11.

TABLE 11 Sequence index n _(oc) (n_(s)) Normal cyclic prefix Extendedcyclic prefix 0 [1 1 1] [1 1] 1 [1 e^(j2π/3) e^(j4π/3)] [1 −1] 2 [1e^(j4π/3) e^(j2π/3)] N/A

FIG. 8 shows PUCCH format 2/2a/2b in case of a normal cyclic prefix.And, FIG. 9 shows PUCCH format 2/2a/2b in case of an extended cyclicprefix.

Referring to FIG. 8 and FIG. 9, in case of a normal CP, a subframe isconstructed with 10 QPSK data symbols as well as RS symbol. Each QPSKsymbol is spread in a frequency domain by CS and is then mapped to acorresponding SC-FDMA symbol. SC-FDMA symbol level CS hopping may beapplied to randomize inter-cell interference. The RS may be multiplexedby CDM using a cyclic shift. For instance, assuming that the number ofavailable CSs is 12, 12 UEs may be multiplexed in the same PRB. Forinstance, assuming that the number of available CSs is 6, 6 UEs may bemultiplexed in the same PRB. In brief, a plurality of UEs in PUCCHformat 1/1 a/1b and PUCCH format 2/2a/2b may be multiplexed by‘CS+OC+PRB’ and ‘CS+PRB’, respectively.

FIG. 10 is a diagram of ACK/NACK channelization for PUCCH formats 1 aand 1b. In particular, FIG. 10 corresponds to a case of ‘Δshift PUCCH=2’

FIG. 11 is a diagram of channelization for a hybrid structure of PUCCHformat 1/1a/1b and PUCCH format 2/2a/2b.

Cyclic shift (CS) hopping and orthogonal cover (OC) remapping may beapplicable in a following manner.

(1) Symbol-based cell-specific CS hopping for randomization ofinter-cell interference

(2) Slot level CS/OC remapping

-   -   1) For inter-cell interference randomization    -   2) Slot based access for mapping between ACK/NACK channel and        resource (k)

Meanwhile, resource nr for PUCCH format 1/1 a/1b may include thefollowing combinations.

(1) CS (=equal to DFT orthogonal code at symbol level) (ncs)

(2) OC (orthogonal cover at slot level) (noc)

(3) Frequency RB (Resource Block) (nrb)

If indexes indicating CS, OC and RB are set to ncs, noc, nrb,respectively, a representative index nr may include ncs, noc and nrb. Inthis case, the nr may meet the condition of ‘nr=(ncs, noc, nrb)’.

The combination of CQI, PMI, RI, CQI and ACK/NACK may be deliveredthrough the PUCCH format 2/2a/2b. And, Reed Muller (RM) channel codingmay be applicable.

For instance, channel coding for UL (uplink) CQI in LTE system may bedescribed as follows. First of all, bitstreams a₀, a₁, a₂, a₃, . . . ,a_(A-1) may be coded using (20, A) RM code. In this case, a₀ and a_(A-1)indicates MSB (Most Significant Bit) and LSB (Least Significant Bit),respectively. In case of an extended cyclic prefix, maximum informationbits include 11 bits except a case that QI and ACK/NACK aresimultaneously transmitted. After coding has been performed with 20 bitsusing the RM code, QPSK modulation may be applied. Before the BPSKmodulation, coded bits may be scrambled.

Table 12 shows a basic sequence for (20, A) code.

TABLE 12 i M_(i, 0) M_(i, 1) M_(i, 2) M_(i, 3) M_(i, 4) M_(i, 5)M_(i, 6) M_(i, 7) M_(i, 8) M_(i, 9) M_(i, 10) M_(i, 11) M_(i, 12) 0 1 10 0 0 0 0 0 0 0 1 1 0 1 1 1 1 0 0 0 0 0 0 1 1 1 0 2 1 0 0 1 0 0 1 0 1 11 1 1 3 1 0 1 1 0 0 0 0 1 0 1 1 1 4 1 1 1 1 0 0 0 1 0 0 1 1 1 5 1 1 0 01 0 1 1 1 0 1 1 1 6 1 0 1 0 1 0 1 0 1 1 1 1 1 7 1 0 0 1 1 0 0 1 1 0 1 11 8 1 1 0 1 1 0 0 1 0 1 1 1 1 9 1 0 1 1 1 0 1 0 0 1 1 1 1 10 1 0 1 0 0 11 1 0 1 1 1 1 11 1 1 1 0 0 1 1 0 1 0 1 1 1 12 1 0 0 1 0 1 0 1 1 1 1 1 113 1 1 0 1 0 1 0 1 0 1 1 1 1 14 1 0 0 0 1 1 0 1 0 0 1 0 1 15 1 1 0 0 1 11 1 0 1 1 0 1 16 1 1 1 0 1 1 1 0 0 1 0 1 1 17 1 0 0 1 1 1 0 0 1 0 0 1 118 1 1 0 1 1 1 1 1 0 0 0 0 0 19 1 0 0 0 0 1 1 0 0 0 0 0 0

Channel coding bits b₀, b₁, b₂, b₃, . . . , b_(B-1) may be generated by[Equation 31].

$\begin{matrix}{b_{i} = {\sum\limits_{n - 0}^{d - 1}\; {\left( {a_{n} \cdot M_{i,n}} \right){mod}\; 2}}} & \left\lbrack {{Equation}\mspace{14mu} 3} \right\rbrack\end{matrix}$

In [Equation 3], ‘i=0, 1, 2, . . . , B−1’ is met.

In case of wideband repots, a bandwidth of UCI (uplink controlinformation) field for CQI/PMI can be represented as Tables 8 to 10 inthe following.

[Table 13] shows UCI (Uplink Control Information) field for broadbandreport (single antenna port, transmit diversity) or open loop spatialmultiplexing PDSCH CQI feedback.

TABLE 13 Field Bandwidth Wideband CQI 4

[Table 14] shows UL control information (UCI) field for CQI and PMIfeedback in case of wideband reports (closed loop spatial multiplexingPDSCH transmission).

TABLE 14 Bandwidth 2 antenna ports 4 antenna ports Field rank = 1 rank =2 rank = 1 Rank > 1 Wideband CQI 4 4 4 4 Spatial differential CQI 0 3 03 Precoding Matrix 2 1 4 4 Indication

[Table 15] shows UL control information (UCI) field for RI feedback incase of wideband reports.

TABLE 15 Bit widths 4 antenna ports Field 2 antenna ports Max. 2 layersMax. 4 layers Rank Indication 1 1 2

FIG. 12 is a diagram for PRB allocation. Referring to FIG. 20, PRB maybe usable for PUCCH transmission in a slot ns.

2. Carrier Aggregation (CA) Environment

2.1 CA Overview

A 3GPP LTE system (conforming to Rel-8 or Rel-9) (hereinafter, referredto as an LTE system) uses Multi-Carrier Modulation (MCM) in which asingle Component Carrier (CC) is divided into a plurality of bands. Incontrast, a 3GPP LTE-A system (hereinafter, referred to an LTE-A system)may use CA by aggregating one or more CCs to support a broader systembandwidth than the LTE system. The term CA is interchangeably used withcarrier combining, multi-CC environment, or multi-carrier environment.

In the present disclosure, multi-carrier means CA (or carriercombining). Herein, CA covers aggregation of contiguous carriers andaggregation of non-contiguous carriers. The number of aggregated CCs maybe different for a DL and a UL. If the number of DL CCs is equal to thenumber of UL CCs, this is called symmetric aggregation. If the number ofDL CCs is different from the number of UL CCs, this is called asymmetricaggregation. The term CA is interchangeable with carrier combining,bandwidth aggregation, spectrum aggregation, etc.

The LTE-A system aims to support a bandwidth of up to 100 MHz byaggregating two or more CCs, that is, by CA. To guarantee backwardcompatibility with a legacy IMT system, each of one or more carriers,which has a smaller bandwidth than a target bandwidth, may be limited toa bandwidth used in the legacy system.

For example, the legacy 3GPP LTE system supports bandwidths {1.4, 3, 5,10, 15, and 20 MHz} and the 3GPP LTE-A system may support a broaderbandwidth than 20 MHz using these LTE bandwidths. A CA system of thepresent disclosure may support CA by defining a new bandwidthirrespective of the bandwidths used in the legacy system.

There are two types of CA, intra-band CA and inter-band CA. Intra-bandCA means that a plurality of DL CCs and/or UL CCs are successive oradjacent in frequency. In other words, the carrier frequencies of the DLCCs and/or UL CCs are positioned in the same band. On the other hand, anenvironment where CCs are far away from each other in frequency may becalled inter-band CA. In other words, the carrier frequencies of aplurality of DL CCs and/or UL CCs are positioned in different bands. Inthis case, a UE may use a plurality of Radio Frequency (RF) ends toconduct communication in a CA environment.

The LTE-A system adopts the concept of cell to manage radio resources.The above-described CA environment may be referred to as a multi-cellenvironment. A cell is defined as a pair of DL and UL CCs, although theUL resources are not mandatory. Accordingly, a cell may be configuredwith DL resources alone or DL and UL resources.

For example, if one serving cell is configured for a specific UE, the UEmay have one DL CC and one UL CC. If two or more serving cells areconfigured for the UE, the UE may have as many DL CCs as the number ofthe serving cells and as many UL CCs as or fewer UL CCs than the numberof the serving cells, or vice versa. That is, if a plurality of servingcells are configured for the UE, a CA environment using more UL CCs thanDL CCs may also be supported.

CA may be regarded as aggregation of two or more cells having differentcarrier frequencies (center frequencies). Herein, the term ‘cell’ shouldbe distinguished from ‘cell’ as a geographical area covered by an eNB.Hereinafter, intra-band CA is referred to as intra-band multi-cell andinter-band CA is referred to as inter-band multi-cell.

In the LTE-A system, a Primacy Cell (PCell) and a Secondary Cell (SCell)are defined. A PCell and an SCell may be used as serving cells. For a UEin RRC_CONNECTED state, if CA is not configured for the UE or the UEdoes not support CA, a single serving cell including only a PCell existsfor the UE. On the contrary, if the UE is in RRC_CONNECTED state and CAis configured for the UE, one or more serving cells may exist for theUE, including a PCell and one or more SCells.

Serving cells (PCell and SCell) may be configured by an RRC parameter. Aphysical-layer ID of a cell, PhysCellId is an integer value ranging from0 to 503. A short ID of an SCell, SCellIndex is an integer value rangingfrom 1 to 7. A short ID of a serving cell (PCell or SCell),ServeCellIndex is an integer value ranging from 1 to 7. IfServeCellIndex is 0, this indicates a PCell and the values ofServeCellIndex for SCells are pre-assigned. That is, the smallest cellID (or cell index) of ServeCellIndex indicates a PCell.

A PCell refers to a cell operating in a primary frequency (or a primaryCC). A UE may use a PCell for initial connection establishment orconnection reestablishment. The PCell may be a cell indicated duringhandover. In addition, the PCell is a cell responsible forcontrol-related communication among serving cells configured in a CAenvironment. That is, PUCCH allocation and transmission for the UE maytake place only in the PCell. In addition, the UE may use only the PCellin acquiring system information or changing a monitoring procedure. AnEvolved Universal Terrestrial Radio Access Network (E-UTRAN) may changeonly a PCell for a handover procedure by a higher layerRRCConnectionReconfiguraiton message including mobilityControlInfo to aUE supporting CA.

An SCell may refer to a cell operating in a secondary frequency (or asecondary CC). Although only one PCell is allocated to a specific UE,one or more SCells may be allocated to the UE. An SCell may beconfigured after RRC connection establishment and may be used to provideadditional radio resources. There is no PUCCH in cells other than aPCell, that is, in SCells among serving cells configured in the CAenvironment.

When the E-UTRAN adds an SCell to a UE supporting CA, the E-UTRAN maytransmit all system information related to operations of related cellsin RRC_CONNECTED state to the UE by dedicated signaling. Changing systeminformation may be controlled by releasing and adding a related SCell.Herein, a higher layer RRCConnectionReconfiguration message may be used.The E-UTRAN may transmit a dedicated signal having a different parameterfor each cell rather than it broadcasts in a related SCell.

After an initial security activation procedure starts, the E-UTRAN mayconfigure a network including one or more SCells by adding the SCells toa PCell initially configured during a connection establishmentprocedure. In the CA environment, each of a PCell and an SCell mayoperate as a CC. Hereinbelow, a Primary CC (PCC) and a PCell may be usedin the same meaning and a Secondary CC (SCC) and an SCell may be used inthe same meaning in embodiments of the present disclosure.

FIG. 13 illustrates an example of CCs and CA in the LTE-A system, whichare used in embodiments of the present disclosure.

FIG. 13(a) illustrates a single carrier structure in the LTE system.There are a DL CC and a UL CC and one CC may have a frequency range of20 MHz.

FIG. 13(b) illustrates a CA structure in the LTE-A system. In theillustrated case of FIG. 13(b), three CCs each having 20 MHz areaggregated. While three DL CCs and three UL CCs are configured, thenumbers of DL CCs and UL CCs are not limited. In CA, a UE may monitorthree CCs simultaneously, receive a DL signal/DL data in the three CCs,and transmit a UL signal/UL data in the three CCs.

If a specific cell manages N DL CCs, the network may allocate M (M≤N) DLCCs to a UE. The UE may monitor only the M DL CCs and receive a DLsignal in the M DL CCs. The network may prioritize L (L≤M≤N) DL CCs andallocate a main DL CC to the UE. In this case, the UE should monitor theL DL CCs. The same thing may apply to UL transmission.

The linkage between the carrier frequencies of DL resources (or DL CCs)and the carrier frequencies of UL resources (or UL CCs) may be indicatedby a higher layer message such as an RRC message or by systeminformation. For example, a set of DL resources and UL resources may beconfigured based on linkage indicated by System Information Block Type 2(SIB2). Specifically, DL-UL linkage may refer to a mapping relationshipbetween a DL CC carrying a PDCCH with a UL grant and a UL CC using theUL grant, or a mapping relationship between a DL CC (or a UL CC)carrying HARQ data and a UL CC (or a DL CC) carrying an HARQ ACK/NACKsignal.

2.2 Cross Carrier Scheduling

Two scheduling schemes, self-scheduling and cross carrier scheduling aredefined for a CA system, from the perspective of carriers or servingcells. Cross carrier scheduling may be called cross CC scheduling orcross cell scheduling.

In self-scheduling, a PDCCH (carrying a DL grant) and a PDSCH aretransmitted in the same DL CC or a PUSCH is transmitted in a UL CClinked to a DL CC in which a PDCCH (carrying a UL grant) is received.

In cross carrier scheduling, a PDCCH (carrying a DL grant) and a PDSCHare transmitted in different DL CCs or a PUSCH is transmitted in a UL CCother than a UL CC linked to a DL CC in which a PDCCH (carrying a ULgrant) is received.

Cross carrier scheduling may be activated or deactivated UE-specificallyand indicated to each UE semi-statically by higher layer signaling (e.g.RRC signaling).

If cross carrier scheduling is activated, a Carrier Indicator Field(CIF) is required in a PDCCH to indicate a DL/UL CC in which aPDSCH/PUSCH indicated by the PDCCH is to be transmitted. For example,the PDCCH may allocate PDSCH resources or PUSCH resources to one of aplurality of CCs by the CIF. That is, when a PDCCH of a DL CC allocatesPDSCH or PUSCH resources to one of aggregated DL/UL CCs, a CIF is set inthe PDCCH. In this case, the DCI formats of LTE Release-8 may beextended according to the CIF. The CIF may be fixed to three bits andthe position of the CIF may be fixed irrespective of a DCI format size.In addition, the LTE Release-8 PDCCH structure (the same coding andresource mapping based on the same CCEs) may be reused.

On the other hand, if a PDCCH transmitted in a DL CC allocates PDSCHresources of the same DL CC or allocates PUSCH resources in a single ULCC linked to the DL CC, a CIF is not set in the PDCCH. In this case, theLTE Release-8 PDCCH structure (the same coding and resource mappingbased on the same CCEs) may be used.

If cross carrier scheduling is available, a UE needs to monitor aplurality of PDCCHs for DCI in the control region of a monitoring CCaccording to the transmission mode and/or bandwidth of each CC.Accordingly, an appropriate SS configuration and PDCCH monitoring areneeded for the purpose.

In the CA system, a UE DL CC set is a set of DL CCs scheduled for a UEto receive a PDSCH, and a UE UL CC set is a set of UL CCs scheduled fora UE to transmit a PUSCH. A PDCCH monitoring set is a set of one or moreDL CCs in which a PDCCH is monitored. The PDCCH monitoring set may beidentical to the UE DL CC set or may be a subset of the UE DL CC set.The PDCCH monitoring set may include at least one of the DL CCs of theUE DL CC set. Or the PDCCH monitoring set may be defined irrespective ofthe UE DL CC set. DL CCs included in the PDCCH monitoring set may beconfigured to always enable self-scheduling for UL CCs linked to the DLCCs. The UE DL CC set, the UE UL CC set, and the PDCCH monitoring setmay be configured UE-specifically, UE group-specifically, orcell-specifically.

If cross carrier scheduling is deactivated, this implies that the PDCCHmonitoring set is always identical to the UE DL CC set. In this case,there is no need for signaling the PDCCH monitoring set. However, ifcross carrier scheduling is activated, the PDCCH monitoring set may bedefined within the UE DL CC set. That is, the eNB transmits a PDCCH onlyin the PDCCH monitoring set to schedule a PDSCH or PUSCH for the UE.

FIG. 14 illustrates a cross carrier-scheduled subframe structure in theLTE-A system, which is used in embodiments of the present disclosure.

Referring to FIG. 14, three DL CCs are aggregated for a DL subframe forLTE-A UEs. DL CC ‘A’ is configured as a PDCCH monitoring DL CC. If a CIFis not used, each DL CC may deliver a PDCCH that schedules a PDSCH inthe same DL CC without a CIF. On the other hand, if the CIF is used byhigher layer signaling, only DL CC ‘A’ may carry a PDCCH that schedulesa PDSCH in the same DL CC ‘A’ or another CC. Herein, no PDCCH istransmitted in DL CC ‘B’ and DL CC ‘C’ that are not configured as PDCCHmonitoring DL CCs.

FIG. 15 is conceptual diagram illustrating a construction of servingcells according to cross-carrier scheduling.

Referring to FIG. 15, an eNB (or BS) and/or UEs for use in a radioaccess system supporting carrier aggregation (CA) may include one ormore serving cells. In FIG. 8, the eNB can support a total of fourserving cells (cells A, B, C and D). It is assumed that UE A may includeCells (A, B, C), UE B may include Cells (B, C, D), and UE C may includeCell B. In this case, at least one of cells of each UE may be composedof P Cell. In this case, P Cell is always activated, and SCell may beactivated or deactivated by the eNB and/or UE.

The cells shown in FIG. 15 may be configured per UE. The above-mentionedcells selected from among cells of the eNB, cell addition may be appliedto carrier aggregation (CA) on the basis of a measurement report messagereceived from the UE. The configured cell may reserve resources forACK/NACK message transmission in association with PDSCH signaltransmission. The activated cell is configured to actually transmit aPDSCH signal and/or a PUSCH signal from among the configured cells, andis configured to transmit CSI reporting and Sounding Reference Signal(SRS) transmission. The deactivated cell is configured not totransmit/receive PDSCH/PUSCH signals by an eNB command or a timeroperation, and CRS reporting and SRS transmission are interrupted.

2.3 Channel State Information (CSI) Feedback on PUCCH

First of all, in the 3GPP LTE system, when a DL reception entity (e.g.,UE) is connected to a DL transmission entity (e.g., BS), the DLreception entity performs measurement on a Reference Signal ReceivedPower (RSRP) of a reference signal transmitted in DL, a quality of areference signal (RSRQ: Reference Signal Received Quality) and the likeat a random time and is then able to make a periodic or even-triggeredreport of a corresponding measurement result to the BS.

Each UE reports a DL channel information in accordance with a DL channelstatus via uplink. A base station is then able to determinetime/frequency resources, MCS (modulation and coding scheme) and thelike appropriate for a data transmission to each UE using the DL channelinformation received from the each UE.

Such Channel State Information (CSI) may include Channel QualityIndicator (CQI), Precoding Matrix Indicator (PMI), Precoder TypeIndication (PTI) and/or Rank Indication (RI). In particular, the CSI maybe transmitted entirely or partially depending on a transmission mode ofeach UE. CQI is determined based on a received signal quality of a UE,which may be generally determined on the basis of a measurement of a DLreference signal. In doing so, a CQI value actually delivered to a basestation may correspond to an MCS capable of providing maximumperformance by maintaining a Block Error Rate (BLER) under 10% in thereceived signal quality measured by a UE.

This channel information reporting may be classified into a periodicreport transmitted periodically and an aperiodic report transmitted inresponse to a request made by a BS.

In case of the aperiodic report, it is set for each UE by a 1-bitrequest bit (CQI request bit) contained in UL scheduling informationdownloaded to a UE by a BS. Having received this information, each UE isthen able to deliver channel information to the BS via a Physical UplinkShared Channel (PUSCH) in consideration of its transmission mode. And,it may set RI and CQI/PMI not to be transmitted on the same PUSCH.

In case of the periodic report, a period for transmitting channelinformation via an upper layer signal, an offset in the correspondingperiod and the like are signaled to each UE by subframe unit and channelinformation in consideration of a transmission mode of each UE may bedelivered to a BS via a Physical Uplink Control Channel (PUCCH) inaccordance with a determined period. In case that data transmitted inuplink simultaneously exists in a subframe in which channel informationis transmitted by a determined period, the corresponding channelinformation may be transmitted together with the data not on the PUCCHbut on a Physical Uplink Shared Channel (PUSCH). In case of the periodicreport via PUCCH, bits (e.g., 11 bits) limited further than those of thePUSCH may be used. RI and CQI/PMI may be transmitted on the same PUSCH.

In case that contention occurs between the periodic report and theaperiodic report in the same subframe, only the aperiodic report can beperformed.

In calculating Wideband CQI/PMI, a most recently transmitted RI may beusable. RI in a PUCCH CSI report mode is independent from RI in a PUSCHCSI report mode. The RI in the PUSCH CSI report mode is valid forCQI/PMI in the corresponding PUSCH CSI report mode only.

Table 16 is provided to describe CSI feedback type transmitted on PUCCHand PUCCH CSI report mode.

TABLE 16 PMI Feedback Type No PMI (OL, TD, single-antenna) Single PMI(CL) CQI Wideband Mode 1-0 Mode 1-1 Feedback RI (only for Open-Loop SM)RI Type One Wideband CQI (4 bit) Wideband CQI (4 bit) when RI > 1, CQIof first codeword Wideband spatial CQI (3 bit) for RI > 1 Wideband PMI(4 bit) UE Mode 2-0 Mode 2-1 Selected RI (only for Open-Loop SM) RIWideband CQI (4 bit) Wideband CQI (4 bit) Best-1 CQI (4 bit) in each BPWideband spatial CQI (3 bit) for RI > 1 Best-1 indicator(L-bit label)Wideband PMI (4 bit) when RI > 1, CQI of first codeword Best-1 CQI (4bit) 1 in each BP Best-1 spatial CQI (3 bit) for RI > 1 Best-1 indicator(L-bit label)

Referring to [Table 16], in the periodic report of channel information,there are 4 kinds of reporting modes (mode 1-0, mode 1-2, mode 2-0 andmode 2-1) in accordance with CQI and PMI feedback types.

CQI can be classified into WideBand (WB) CQI and SubBand (SB) CQI inaccordance with CQI feedback type and PMI can be classified into No PMIor Single PMI in accordance with a presence or non-presence of PMItransmission. In Table 11, No PMI corresponds to a case of Open-Loop(OL), Transmit Diversity (TD) and single-antenna, while Single PMIcorresponds to a case of Closed-Loop (CL).

The mode 1-0 corresponds to a case that WB CQI is transmitted in theabsence of PMI transmission. In this case, RI is transmitted only incase of OL Spatial Multiplexing (SM) and one WB CQI represented as 4bits can be transmitted. If RI is greater than 1, CQI for a 1st codewordcan be transmitted.

Mode 1-1 corresponds to a case that a single PMI and WB CQI aretransmitted. In this case, 4-bit WB CQI and 4-bit WB PMI can betransmitted together with RI transmission. Additionally, if RI isgreater than 1, 3-bit WB (wideband) spatial differential CQI can betransmitted. In 2-codeword transmission, the WB spatial differential CQImay indicate a difference value between a WB CQI index for codeword 1and a WB CQI index for codeword 2. The difference value in-between mayhave a value selected from a set {−4, −3, −2, −1, 0, 1, 2, 3} and can berepresented as 3 bits.

The mode 2-0 corresponds to a case that CQI on a UE-selected band istransmitted in the absence of PMI transmission. In this case, RI istransmitted only in case of open-loop spatial multiplexing (SM) and a WBCQI represented as 4 bits may be transmitted. A best CQI (best-1) istransmitted on each bandwidth part (BP) and the best-1 CQI may berepresented as 4 bits. And, an L-bit indicator indicating the best-1 maybe transmitted together. If the RI is greater than 1, a CQI for a 1stcodeword can be transmitted.

And, Mode 2-1 corresponds to a case that a single PMI and a CQI on aUE-selected band are transmitted. In this case, together with RItransmission, 4-bit WB CQI, 3-bit WB spiral differential CQI and 4-bitWB PMI can be transmitted. Additionally, 4-bit best-1 CQI is transmittedon each Bandwidth Part (BP) and L-bit best-1 indicator can betransmitted together. Additionally, if RI is greater than 1, 3-bitbest-1 spatial differential CQI can be transmitted. In 2-codewordtransmission, it may indicate a difference value between a best-1 CQIindex of codeword 1 and a best-1 CQI index of codeword 2.

For the transmission modes, periodic PUCCH CSI report modes aresupported as follows.

1) Transmission mode 1: Modes 1-0 and 2-0

2) Transmission mode 2: Modes 1-0 and 2-0

3) Transmission mode 3: Modes 1-0 and 2-0

4) Transmission mode 4: Modes 1-1 and 2-1

5) Transmission mode 5: Modes 1-1 and 2-1

6) Transmission mode 6: Modes 1-1 and 2-1

7) Transmission mode 7: Modes 1-0 and 2-0

8) Transmission mode 8: Modes 1-1 and 2-1 if a UE is set to make aPMI/RI reporting, or Modes 1-0 and 2-0 if a UE is set not to make aPMI/RI reporting

9) Transmission mode 9: Modes 1-1 and 2-1 if a UE is set to make aPMT/RI reporting and the number of CSI-RS ports is greater than 1, orModes 1-0 and 2-0 if a UE is set not to make a PMI/RI reporting and thenumber of CSI-RS port(s) is equal to 1.

The periodic PUCCH CSIU reporting mode in each serving cell is set byupper layer signaling. And, Mode 1-1 is set to either submode 1 orsubmode 2 by an upper layer signaling using a parameter‘PUCCH_format1-1_CSI_reporting_mode’.

A CQI reporting in a specific subframe of a specific serving cell in aUE-selected SB CQI means a measurement of at least one channel state ofa bandwidth part (BP) corresponding to a portion of a bandwidth of aserving cell. An index is given to the bandwidth part in a frequencyincreasing order starting with a lowest frequency without an incrementof a bandwidth.

2.4 Method for Transmitting ACK/NACK on PUCCH

2.4.1 ACK/NACK Transmission in LTE System

Under the situation that a UE simultaneously transmits a plurality ofACKs/NACKs corresponding to multiple data units received from an eNB, inorder to maintain the single-carrier property of ACK/NACK signals andreduce the total ACK/NACK transmission power, ACK/NACK multiplexingmethod based on PUCCH resource selection can be considered. WithACK/NACK multiplexing, contents of the ACK/NACK signals for multipledata units are identified by the combination of the PUCCH resource usedin actual ACK/NACK transmission and the one of QPSK modulation symbols.For example, if it is assumed that one PUCCH resource carries 4 bits and4 data units can be transmitted in maximum (at this time, assume thatHARQ operation for each data unit can be managed by single ACK/NACKbit), the Transmission (Tx) node can identify the ACK/NACK result basedon the transmission position of the PUCCH signal and the bits of theACK/NACK signal as shown in [Table 17] below.

TABLE 17 HARQ-ACK(0), HARQ-ACK(1), b(0), HARQ-ACK(2), HARQ-ACK(3)n_(PUCCH) ⁽¹⁾ b(1) ACK, ACK, ACK, ACK n_(PUCCH, 1) ⁽¹⁾ 1, 1 ACK, ACK,ACK, NACK/DTX n_(PUCCH, 1) ⁽¹⁾ 1, 0 NACK/DTX, NACK/DTX, NACK, DTXn_(PUCCH, 2) ⁽¹⁾ 1, 1 ACK, ACK, NACK/DTX, ACK n_(PUCCH, 1) ⁽¹⁾ 1, 0NACK, DTX, DTX, DTX n_(PUCCH, 0) ⁽¹⁾ 1, 0 ACK, ACK, NACK/DTX, NACK/DTXn_(PUCCH, 1) ⁽¹⁾ 1, 0 ACK, NACK/DTX, ACK, ACK n_(PUCCH, 3) ⁽¹⁾ 0, 1NACK/DTX, NACK/DTX, NACK/DTX, NACK n_(PUCCH, 3) ⁽¹⁾ 1, 1 ACK, NACK/DTX,ACK, NACK/DTX n_(PUCCH, 2) ⁽¹⁾ 0, 1 ACK, NACK/DTX, NACK/DTX, ACKn_(PUCCH, 0) ⁽¹⁾ 0, 1 ACK, NACK/DTX, NACK/DTX, NACK/DTX n_(PUCCH, 0) ⁽¹⁾1, 1 NACK/DTX, ACK, ACK, ACK n_(PUCCH, 3) ⁽¹⁾ 0, 1 NACK/DTX, NACK, DTX,DTX n_(PUCCH, 1) ⁽¹⁾ 0, 0 NACK/DTX, ACK, ACK, NACK/DTX n_(PUCCH, 2) ⁽¹⁾1, 0 NACK/DTX, ACK, NACK/DTX, ACK n_(PUCCH, 3) ⁽¹⁾ 1, 0 NACK/DTX, ACK,NACK/DTX, NACK/DTX n_(PUCCH, 1) ⁽¹⁾ 0, 1 NACK/DTX, NACK/DTX, ACK, ACKn_(PUCCH, 3) ⁽¹⁾ 0, 1 NACK/DTX, NACK/DTX, ACK, NACK/DTX n_(PUCCH, 2) ⁽¹⁾0, 0 NACK/DTX, NACK/DTX, NACK/DTX, ACK n_(PUCCH, 3) ⁽¹⁾ 0, 0 DTX, DTX,DTX, DTX N/A N/A

In [Table 17], HARQ-ACK(i) indicates the ACK/NACK result for the dataunit i. For example, if a maximum of 4 data units is transmitted, i=0,1, 2, 3. In Table 17, DTX means that there is no data unit transmittedfor corresponding HARQ-ACK(i) or the Reception (Rx) node doesn't detectthe existence of the data unit corresponding to HARQ-ACK(i).

In addition, n_(PUCCH,X) ⁽¹⁾ indicates the PUCCH resource which shouldbe used in actual ACK/NACK transmission, if there are 4 PUCCH resources,a maximum of four PUCCH resources n_(PUCCH,0) ⁽¹⁾, n_(PUCCH,1) ⁽¹⁾,n_(PUCCH,2) ⁽¹⁾ and n_(PUCCH,3) ⁽¹⁾ may be allocated to the UE.

In addition, b(0), b(1) indicates two bits carried by the selected PUCCHresource. Modulation symbols which are transmitted through PUCCHresource are decided according to the bits. For example, if the RX nodereceives and decodes 4 data units successfully, the RX node shouldtransmit two bits, (1, 1), using PUCCH resource n_(PUCCH,1) ⁽¹⁾. Foranother example, if the RX node receives 4 data units and fails indecoding the first and the third data units (corresponding toHARQ-ACK(0) and HARQ-ACK(2)), the RX node should transmit (1, 0) usingn_(PUCCH,3) ⁽¹⁾.

By linking the actual ACK/NACK contents with the combination of PUCCHresource selection and the actual bit contents in the transmitted PUCCHresource in this way, ACK/NACK transmission using a single PUCCHresource for multiple data units is possible.

In ACK/NACK multiplexing method (see Table 17), basically, NACK and DTXare coupled as NACK/DTX if at least one ACK exists for all data units.This is because combinations of PUCCH resources and QPSK symbols areinsufficient to cover all ACK, NACK and DTX hypotheses. On the otherhand, for the case that no ACK exists for all data units (in otherwords, NACK or DTX only exists for all data units), single NACKdecoupled with DTX is defined one as HARQ-ACK(i). In this case, PUCCHresource linked to the data unit corresponding to single NACK can bealso reserved to transmit the signal of multiple ACKs/NACKs.

2.4.2 ACK/NACK Transmission in LTE-A System

In an LTE-A system (e.g., Rel-10, 11, 12, etc.), transmission of aplurality of ACK/NACK signals for a plurality of PDSCH signals, which istransmitted via a plurality of DL CCs, via a specific UL CC isconsidered. Unlike ACK/NACK transmission using PUCCH format 1a/1b of anLTE system, a plurality of ACK/NACK signals may be subjected to channelcoding (e.g., Reed-Muller coding, Tail-biting convolutional coding,etc.) and then a plurality of ACK/NACK information/signals may betransmitted using PUCCH format 2 or a new PUCCH format (e.g., an E-PUCCHformat) modified based on block spreading.

FIG. 16 shows an example of a new PUCCH format based on block spreading.

A block spreading scheme refers to a method for performing modulationusing an SC-FDMA scheme unlike PUCCH format series 1 or 2 in an LTEsystem. The block spreading scheme refers to a scheme for time-domainspreading and transmitting a symbol sequence using an Orthogonal CoverCode (OCC) as shown in FIG. 16. That is, the symbol sequence is spreadusing the OCC to multiplex control signals of several UEs in the sameRB.

In the above-described PUCCH format 2, one symbol sequence istransmitted over the time domain and UE multiplexing is performed usingCyclic Shift (CCS) of a CAZAC sequence. However, in the new PUCCH formatbased on block spreading, one symbol sequence is transmitted over thefrequency domain and UE multiplexing is performed using time-domainspreading based on an OCC.

For example, as shown in FIG. 16, one symbol sequence may be generatedas five SC-FDMA symbols by an OCC of length-5 (that is, SF=5). Althougha total of 2 RS symbols is used during one slot in FIG. 16, variousmethods using three RS symbols and using an OCC of SF=4 may be used. Atthis time, the RS symbols may be generated from a CAZAC sequence havingspecific cyclic shift and may be transmitted in the form in which aspecific OCC is applied (multiplied by) to a plurality of RS symbols ofthe time domain.

In the embodiments of the present invention, for convenience ofdescription, a multi-ACK/NACK transmission scheme based on channelcoding using PUCCH format 2 or a new PUCCH format (e.g., an E-PUCCHformat) is defined as a “multi-bit ACK/NACK coding transmission method”.

The multi-bit ACK/NACK coding method refers to a method for transmittingACK/NACK code blocks generated by channel-coding ACK/NACK or DTXinformation (meaning that the PDCCH is not received/detected) for PDSCHsignals transmitted on a plurality of DL CCs.

For example, when the UE operates on a certain DL CC in an SU-MIMO modeand receives two CodeWords (CW), the UE may have a maximum of fivefeedback states including a total of four feedback states of each CW,such as ACK/ACK, ACK/NACK, NACK/ACK and NACK/NACK, and DTX. When the UEreceives a single CW, the UE may have a maximum of three statesincluding ACK, NACK and/or DTX. When NACK and DTX are equally processed,the UE may have a total of two states such as ACK and NACK/DTX.

Accordingly, when the UE aggregates a maximum of five DL CCs and the UEoperates on all DL CCs in an SU-MIMO mode, the UE may have a maximum of55 transmittable feedback states. At this time, the size of ACK/NACKpayload representing the 55 feedback states may be a total of 12 bits.If DTX and NACK are equally processed, the number of feedback statesbecomes 45 and the size of the ACK/NACK payload representing thefeedback states is a total of 10 bits.

In an ACK/NACK multiplexing (that is, ACK/NACK selection) method appliedto an LTE TDD system, fundamentally, an implicit ACK/NACK selectionmethod in which an implicit PUCCH resource corresponding to a PDCCHscheduling each PDSCH (that is, linked to a smallest CCE index) is usedfor ACK/NACK transmission in order to secure a PUCCH resource of eachUE.

In an LTE-A FDD system, transmission of a plurality of ACK/NACK signalsfor a plurality of PDSCH signals transmitted via a plurality of DL CCsvia one UE-specific UL CC is considered. “ACK/NACK selection” methodsusing an implicit PUCCH resource linked to a PDCCH scheduling some orall DL CCs (that is, linked to a smallest CCE index nCCE or linked tonCCE and nCCE+1) or a combination of an implicit PUCCH and an explicitPUCCH resource pre-allocated to each UE via RRC signaling areconsidered.

Even in an LTE-A TDD system, aggregation of a plurality of CCs isconsidered. For example, when a plurality of CCs is aggregated, UEtransmitting a plurality of ACK/NACK information/signals for a pluralityof PDSCH signals transmitted via a plurality of DL subframes and aplurality of CCs via a specific CC (that is, AN CC) in UL subframescorresponding to the plurality of DL subframes in which the PDSCHsignals are transmitted is considered.

At this time, unlike LTE-A FDD, a method (that is, full ACK/NACK) fortransmitting a plurality of ACK/NACK signals corresponding to a maximumnumber of CWs, which may be transmitted via all CCs allocated to the UE,for a plurality of DL subframes may be considered or a method (that is,bundled ACK/NACK) for applying ACK/NACK bundling to a CW, CC and/or asubframe region, reducing the number of transmitted ACKs/NACKs andperforming transmission may be considered.

At this time, CW bundling means that ACK/NACK bundling for CW per CC isapplied to each DL subframe and CC bundling means that ACK/NACK bundlingfor all or some CCs is applied to each DL subframe. In addition,subframe bundling means that ACK/NACK bundling for all or some DLsubframes is applied to each CC.

As the subframe bundling method, an ACK counter method indicating atotal number of ACKs (or the number of some ACKs) per CC for all PDSCHsignals or DL grant PDCCHs received on each DL CC may be considered. Atthis time, the multi-bit ACK/NACK coding scheme or the ACK/NACKtransmission scheme based on the ACK/NACK selection method may beconfigurably applied according to the size of the ACK/NACK payload perUE, that is, the size of the ACK/NACK payload for transmission of fullor bundled ACK/NACK configured per UE.

2.5 Procedure for Transmitting and Receiving PUCCH

In a mobile communication system, one eNB transmits and receives data toand from a plurality of UEs via a wireless channel environment in onecell/sector. In a system operating using multiple carriers or the like,the eNB receives packet traffic from a wired Internet network andtransmits the received packet traffic to each UE using a predeterminedcommunication scheme. At this time, downlink scheduling is how the eNBdetermines when data is transmitted to which UE using which frequencydomain. In addition, the eNB receives and demodulates data from the UEusing a predetermined communication scheme and transmits packet trafficover a wired Internet network. Uplink scheduling is how the eNBdetermines when to enable which UE to transmit uplink data using whichfrequency domain. In general, a UE having a good channel state maytransmit and receive data using more time and frequency resources.

In a system operating using multiple carriers or the like, resources maybe roughly divided into a time domain and a frequency domain. Theresources may be defined as resource blocks, which includes Nsubcarriers and M subframes or predetermined time units. At this time, Nand M may be 1. FIG. 17 is a diagram showing an example of configuring aresource block in time-frequency units.

In FIG. 17, one rectangle means one resource block and one resourceblock has several subcarriers on one axis and has a predetermined timeunit (e.g., slots or subframes) on the other axis.

In downlink, an eNB schedules one or more resource blocks to a UEselected according to a determined scheduling rule and transmits datausing resource bocks allocated to the UE. In uplink, the eNB schedulesone or more resource blocks to a UE selected according to apredetermined scheduling rule and a UE transmits data in uplink usingthe allocated resources.

An error control method performed when a (sub)frame, in which data istransmitted and received, is lost or damaged after transmitting andreceiving data after scheduling includes an Automatic Repeat reQuest(ARQ) method and a Hybrid ARQ (HARQ) method.

In the ARQ method, fundamentally, a transmitter waits for anacknowledgement (ACK) message after transmitting one (sub)frame and areceiver sends the ACK only upon receiving the sub(frame). When an erroroccurs in the (sub)frame, a negative ACK (NAK) message is sent andinformation on a reception frame, in which an error occurs, is removedfrom a receiver buffer. The transmitter transmits a subsequent(sub)frame upon receiving the ACK message but retransmits the (sub)frameupon receiving the NAK message. Unlike the ARQ method, in the HARQmethod, when the received frame cannot be demodulated, the receivertransmits the NAK message to the transmitter, but the received frame isstored in a buffer during a predetermined time and is combined with aretransmitted frame, thereby increasing a reception success rate.

Recently, a HARQ method more efficient than the ARQ method is widelyused. The HARQ method may be divided into various methods. For example,the HARQ method may be divided into a synchronous HARQ method and anasynchronous HARQ method according to retransmission timing and into achannel-adaptive HARQ method and a channel-non-adaptive HARQ methoddepending on whether the amount of resources used for retransmission isinfluenced by a channel state.

The synchronous HARQ method refers to a method of performing subsequentretransmission at timing determined by a system when initialtransmission fails. For example, if it is assumed that retransmission isperformed every four time units after initial transmission fails,retransmission timing is predetermined between the eNB and the UE and isnot signaled. However, when the data transmission side receives a NAKmessage, the frame is retransmitted every four time units until an ACKmessage is received.

Meanwhile, the asynchronous HARQ method may be performed by newlyscheduling retransmission timing or via additional signaling. Theretransmission timing of the previously failed frame may be changed byseveral factors such as channel state.

The channel-non-adaptive HARQ method refers to a method of usingscheduling information (e.g., the modulation method of the frame, thenumber of used resource blocks, Adaptive Modulation and Coding (AMC),etc.), which is set upon initial transmission, upon retransmission. Incontrast, the channel-adaptive HARQ method refers to a method ofchanging such scheduling information according to the channel state.

For example, in the channel-non-adaptive HARQ method, a transmissionside transmits data using six resource blocks upon initial transmissionand retransmits data using six resource blocks upon retransmission. Incontrast, in the channel-adaptive HARQ method, initial transmission isperformed using six resource blocks and retransmission is performedusing greater or less than six resource blocks according to the channelstate.

Although there are four HARQ methods, the asynchronous andchannel-adaptive HARQ method and the synchronous andchannel-non-adaptive HARQ method are mainly used. The asynchronous andchannel-adaptive HARQ method may maximize retransmission efficiency byadaptively changing the retransmission timing and the amount of usedresources according to the channel state but may increase overhead.Accordingly, the asynchronous and channel-adaptive HARQ method is notgenerally considered for uplink. In contrast, the synchronous andchannel-non-adaptive HARQ method may not cause overhead becauseretransmission timing and resource allocation are predetermined in thesystem, but has very low retransmission efficiency in a considerablychanged channel state.

To this end, in the current 3GPP LTE/LTE-A system, the asynchronous HARQmethod is used in downlink and the synchronous HARQ method is used inuplink.

FIG. 18 is a diagram showing an example of a resource allocation andretransmission method of an asynchronous HARQ method.

When an eNB transmits scheduling information in downlink, receivesACK/NAK information from a UE, and transmits next data, time delayoccurs as shown in FIG. 19. This is channel propagation delay and delayoccurring due to a time required for data decoding and data encoding.

A method of performing transmission using an independent HARQ processfor data transmission without a gap during a delay period is being used.For example, if a shortest period from first data transmission to nextdata transmission is 7 subframes, data may be transmitted without a gapby setting 7 independent HARQ processes. In an LTE/LTE-A system, amaximum of eight HARQ processes may be allocated to one UE in non-MIMO.

2.6 CA Environment-Based CoMP Operation

Hereinafter, a cooperation multi-point (CoMP) transmission operationapplicable to the embodiments of the present disclosure will bedescribed.

In the LTE-A system, CoMP transmission may be implemented using acarrier aggregation (CA) function in the LTE. FIG. 19 is a conceptualview illustrating a CoMP system operating based on a CA environment.

In FIG. 19, it is assumed that a carrier operated as a PCell and acarrier operated as an SCell may use the same frequency band on afrequency axis and are allocated to two eNBs geographically spaced apartfrom each other. At this time, a serving eNB of UE1 may be allocated tothe PCell, and a neighboring cell causing much interference may beallocated to the SCell. That is, the eNB of the PCell and the eNB of theSCell may perform various DL/UL CoMP operations such as jointtransmission (JT), CS/CB and dynamic cell selection for one UE.

FIG. 19 illustrates an example that cells managed by two eNBs areaggregated as PCell and SCell with respect to one UE (e.g., UE1).However, as another example, three or more cells may be aggregated. Forexample, some cells of three or more cells may be configured to performCoMP operation for one UE in the same frequency band, and the othercells may be configured to perform simple CA operation in differentfrequency bands. At this time, the PCell does not always need toparticipate in CoMP operation.

2.7 Reference Signal (RS)

Now, a description will be given of RSs which may be used in embodimentsof the present disclosure.

FIG. 20 illustrates an example of a subframe to which UE-RSs areallocated, which may be used in embodiments of the present disclosure.

Referring to FIG. 20, the subframe illustrates REs occupied by UE-RSsamong REs in one RB of a normal DL subframe having a normal CP.

UE-RSs are transmitted on antenna port(s) p=5, p=7, p=8 or p=7, 8, . . ., υ+6 for PDSCH transmission, where υ is the number of layers used forthe PDSCH transmission. UE-RSs are present and are a valid reference forPDSCH demodulation only if the PDSCH transmission is associated with thecorresponding antenna port. UE-RSs are transmitted only on RBs to whichthe corresponding PDSCH is mapped.

The UE-RSs are configured to be transmitted only on RB(s) to which aPDSCH is mapped in a subframe in which the PDSCH is scheduled unlikeCRSs configured to be transmitted in every subframe irrespective ofwhether the PDSCH is present. Accordingly, overhead of the RS maydecrease relative to overhead of the CRS.

In the 3GPP LTE-A system, the UE-RSs are defined in a PRB pair.Referring to FIG. 19, in a PRB having frequency-domain index nPRBassigned for PDSCH transmission with respect to p=7, p=8, or p=7,8, . .. , υ+6, a part of UE-RS sequence r(m) is mapped to complex-valuedmodulation symbols.

UE-RSs are transmitted through antenna port(s) correspondingrespectively to layer(s) of a PDSCH. That is, the number of UE-RS portsis proportional to a transmission rank of the PDSCH. Meanwhile, if thenumber of layers is 1 or 2, 12 REs per RB pair are used for UE-RStransmission and, if the number of layers is greater than 2, 24 REs perRB pair are used for UE-RS transmission. In addition, locations of REsoccupied by UE-RSs (i.e. locations of UE-RS REs) in a RB pair are thesame with respect to a UE-RS port regardless of a UE or a cell.

As a result, the number of DM-RS REs in an RB to which a PDSCH for aspecific UE in a specific subframe is mapped is the same per UE-RSports. Notably, in RBs to which the PDSCH for different UEs in the samesubframe is allocated, the number of DM-RS REs included in the RBs maydiffer according to the number of transmitted layers.

The UE-RS can be used as the DM-RS in the embodiments of the presentdisclosure.

2.8 Enhanced PDCCH (EPDCCH)

In the 3GPP LTE/LTE-A system, Cross-Carrier Scheduling (CCS) in anaggregation status for a plurality of component carriers (CC: componentcarrier=(serving) cell) will be defined. One scheduled CC may previouslybe configured to be DL/UL scheduled from another one scheduling CC (thatis, to receive DL/UL grant PDCCH for a corresponding scheduled CC). Atthis time, the scheduling CC may basically perform DL/UL scheduling foritself. In other words, a Search Space (SS) for a PDCCH for schedulingscheduling/scheduled CCs which are in the CCS relation may exist in acontrol channel region of all the scheduling CCs.

Meanwhile, in the LTE system, FDD DL carrier or TDD DL subframes areconfigured to use first n (n<=4) OFDM symbols of each subframe fortransmission of physical channels for transmission of various kinds ofcontrol information, wherein examples of the physical channels include aPDCCH, a PHICH, and a PCFICH. At this time, the number of OFDM symbolsused for control channel transmission at each subframe may be deliveredto the UE dynamically through a physical channel such as PCFICH orsemi-statically through RRC signaling.

Meanwhile, in the LTE/LTE-A system, since a PDCCH which is a physicalchannel for DL/UL scheduling and transmitting various kinds of controlinformation has a limitation that it is transmitted through limited OFDMsymbols, enhanced PDCCH (i.e., E-PDCCH) multiplexed with a PDSCH morefreely in a way of FDM/TDM may be introduced instead of a controlchannel such as PDCCH, which is transmitted through OFDM symbol andseparated from PDSCH. FIG. 21 illustrates an example that legacy PDCCH,PDSCH and E-PDCCH, which are used in an LTE/LTE-A system, aremultiplexed.

3. LTE-U System

3.1 LTE-U System Configuration

Hereinafter, methods for transmitting and receiving data in a CAenvironment of an LTE-A band corresponding to a licensed band and anunlicensed band will be described. In the embodiments of the presentdisclosure, an LTE-U system means an LTE system that supports such a CAstatus of a licensed band and an unlicensed band. A WiFi band orBluetooth (BT) band may be used as the unlicensed band.

FIG. 22 illustrates an example of a CA environment supported in an LTE-Usystem.

Hereinafter, for convenience of description, it is assumed that a UE isconfigured to perform wireless communication in each of a licensed bandand an unlicensed band by using two CCs. The methods which will bedescribed hereinafter may be applied to even a case where three or moreCCs are configured for a UE.

In the embodiments of the present disclosure, it is assumed that acarrier of the licensed band may be a primary CC (PCC or PCell), and acarrier of the unlicensed band may be a secondary CC (SCC or SCell).However, the embodiments of the present disclosure may be applied toeven a case where a plurality of licensed bands and a plurality ofunlicensed bands are used in a carrier aggregation method. Also, themethods suggested in the present disclosure may be applied to even a3GPP LTE system and another system.

In FIG. 22, one eNB supports both a licensed band and an unlicensedband. That is, the UE may transmit and receive control information anddata through the PCC which is a licensed band, and may also transmit andreceive control information and data through the SCC which is anunlicensed band. However, the status shown in FIG. 22 is only example,and the embodiments of the present disclosure may be applied to even aCA environment that one UE accesses a plurality of eNBs.

For example, the UE may configure a macro eNB (M-eNB) and a PCell, andmay configure a small eNB (S-eNB) and an SCell. At this time, the macroeNB and the small eNB may be connected with each other through abackhaul network.

In the embodiments of the present disclosure, the unlicensed band may beoperated in a contention-based random access method. At this time, theeNB that supports the unlicensed band may perform a Carrier Sensing (CS)procedure prior to data transmission and reception. The CS proceduredetermines whether a corresponding band is reserved by another entity.

For example, the eNB of the SCell checks whether a current channel isbusy or idle. If it is determined that the corresponding band is idlestate, the eNB may transmit a scheduling grant to the UE to allocate aresource through (E)PDCCH of the PCell in case of a cross carrierscheduling mode and through PDCCH of the SCell in case of aself-scheduling mode, and may try data transmission and reception.

At this time, the eNB may configure a TxOP including N consecutivesubframes. In this case, a value of N and a use of the N subframes maypreviously be notified from the eNB to the UE through higher layersignaling through the PCell or through a physical control channel orphysical data channel.

3.2 Carrier Sensing (CS) Procedure

In embodiments of the present disclosure, a CS procedure may be called aClear Channel Assessment (CCA) procedure. In the CCA procedure, it maybe determined whether a channel is busy or idle based on a predeterminedCCA threshold or a CCA threshold configured by higher-layer signaling.For example, if energy higher than the CCA threshold is detected in anunlicensed band, SCell, it may be determined that the channel is busy oridle. If the channel is determined to be idle, an eNB may start signaltransmission in the SCell. This procedure may be referred to as LBT.

FIG. 23 is a view illustrating an exemplary Frame Based Equipment (FBE)operation as one of LBT operations.

The European Telecommunication Standards Institute (ETSI) regulation (EN301 893 V1.7.1) defines two LBT operations, Frame Based Equipment (FBE)and Load Based Equipment (LBE). In FBE, one fixed frame is comprised ofa channel occupancy time (e.g., 1 to 10 ms) being a time period duringwhich a communication node succeeding in channel access may continuetransmission, and an idle period being at least 5% of the channeloccupancy time, and CCA is defined as an operation for monitoring achannel during a CCA slot (at least 20 μs) at the end of the idleperiod.

A communication node periodically performs CCA on a per-fixed framebasis. If the channel is unoccupied, the communication node transmitsdata during the channel occupancy time. On the contrary, if the channelis occupied, the communication node defers the transmission and waitsuntil the CCA slot of the next period.

FIG. 24 is a block diagram illustrating the FBE operation.

Referring to FIG. 24, a communication node (i.e., eNB) managing an SCellperforms CCA during a CCA slot. If the channel is idle, thecommunication node performs data Transmission (Tx). If the channel isbusy, the communication node waits for a time period calculated bysubtracting the CCA slot from a fixed frame period, and then resumesCCA.

The communication node transmits data during the channel occupancy time.Upon completion of the data transmission, the communication node waitsfor a time period calculated by subtracting the CCA slot from the idleperiod, and then resumes CCA. If the channel is idle but thecommunication node has no transmission data, the communication nodewaits for the time period calculated by subtracting the CCA slot fromthe fixed frame period, and then resumes CCA.

FIG. 25 is a view illustrating an exemplary LBE operation as one of theLBT operations.

Referring to FIG. 25(a), in LBE, the communication node first sets q (qE {4, 5, . . . , 32}) and then performs CCA during one CCA slot.

FIG. 25(b) is a block diagram illustrating the LBE operation. The LBEoperation will be described with reference to FIG. 15(b).

The communication node may perform CCA during a CCA slot. If the channelis unoccupied in a first CCA slot, the communication node may transmitdata by securing a time period of up to (13/32)q ms.

On the contrary, if the channel is occupied in the first CCA slot, thecommunication node selects N (Nϵ{1, 2, . . . , q}) arbitrarily (i.e.,randomly) and stores the selected N value as an initial count. Then, thecommunication node senses a channel state on a CCA slot basis. Each timethe channel is unoccupied in one specific CCA slot, the communicationnode decrements the count by 1. If the count is 0, the communicationnode may transmit data by securing a time period of up to (13/32)q ms.

3.3. Discontinuous Transmission (DTX) on DL

DTX in an unlicensed carrier having a limited maximum transmissionperiod may affect some functions required for operations of the LTEsystem. These functions may be supported by one or more signalstransmitted at the start of a discontinuous LAA DL transmission. Thefunctions supported by these signals include Automatic Gain Control(AGC) setting, channel reservation, and so on.

In a signal transmission of an LAA node, channel reservation refers totransmission of signals on channels acquired for signal transmission toother nodes after channel access through a successful LBT operation.

Functions supported by one or more signals for LAA operations includingDL DTX include detection of an LAA DL transmission at a UE, and time andfrequency synchronization of UEs. Requirements for these functions donot mean exclusion of other available functions, and these functions maybe supported by other methods.

3.3.1 Time and Frequency Synchronization

A design purpose recommended for the LAA system is to supportacquisition of time and frequency synchronization at a UE by a discoverysignal for Radio Resource Management (RRM) measurement, each of RSsincluded in a DL transmission burst, or a combination of them. Adiscovery signal for RRM measurement, transmitted by a serving cell isused at least for coarse time or frequency synchronization.

3.3.3 DL Transmission Timing

In a DL LAA design, a SubFrame (SF) boundary may be adjusted based on aCA timing relationship between serving cells aggregated by CA defined inan LTE system (Rel-12 or below). However, this does not mean that an eNBstarts a DL transmission only at an SF boundary. The LAA system maysupport a PDSCH transmission even though none of the OFDM symbols of oneSF are available according to a result of an LBT operation. Herein,transmission of control information required for the PDSCH transmissionshould be supported.

3.4. RRM Measurement and Reporting

The LTE-A system may transmit a discovery signal at the start ofsupporting RRM functions including cell detection. The discovery signalmay be referred to as a Discovery Reference Signal (DRS). To support theRRM functions for LAA, the discovery signal, and the transmission andreception functions of the LTE-A system may be modified and thenapplied.

3.4.1 DRS

The DRS of the LTE-A system was designed to support a small cell on-offoperation. Off-small cells refer to small cells in a state where mostfunctions except for periodic DRS transmission are deactivated. DRSs aretransmitted with a periodicity of 40, 80, or 160 ms in a DRStransmission occasion. A Discovery Measurement Timing Configuration(DMTC) is a time period during which a UE may expect to receive a DRS. ADRS transmission occasion may occur anywhere within a DMTC, and the UEmay expect that the DRS will be transmitted with a correspondingperiodicity in an allocated cell.

The use of the DRS of the LTE-A system in the LAA system may bring aboutnew constraints. For example, although a DRS transmission may be allowedin some regions, like a very short control transmission without LBT, ashort control transmission without LBT may not be allowed in otherregions. Accordingly, a DRS transmission may be subjected to LBT in theLAA system.

If LBT is applied to a DRS transmission, the DRS may not be transmittedperiodically, as is done in the LTE-A system. Therefore, the followingtwo methods may be considered for DRS transmissions in the LAA system.

First, the DRS is transmitted only at fixed time positions within aconfigured DMTC under the condition of LBT.

Secondly, a DRS transmission is allowed at at least one different timeposition within a configured DMTC under the condition of LBT.

In another aspect of the second method, the number of time positions maybe restricted to 1 within one SF. Aside from a DRS transmission within aconfigured DMTC, a DRS transmission outside the configured DMTC may beallowed, if it is more useful.

FIG. 26 is a view illustrating DRS transmission methods supported in theLAA system.

Referring to FIG. 26, the upper part represents the above-describedfirst DRS transmission method, and the lower part represents the secondDRS transmission method. That is, a UE may receive the DRS only at apredetermined position within a DMTC period in the first DRStransmission method, whereas the UE may receive the DRS at any positionwithin a DMTC period in the second DRS transmission method.

If a UE performs RRM measurement based on a DRS transmission in theLTE-A system, the UE may perform one RRM measurement based on aplurality of DRS occasions. If the DRS is used in the LAA system,transmission of the DRS at a specific position may not be ensured due toLBT-caused constraints. If the UE assumes the existence of the DRS inspite of non-transmission of the DRS from an eNB, the quality of an RRMmeasurement result reported by the UE may be degraded. Therefore, theLAA DRS should be designed such that the existence of the DRS in one DRSoccasion has to be detected, which may ensure the UE to combine thesuccessfully detected DRS occasions for the RRM measurement.

Signals including DRSs do not ensure adjacent DRS transmissions in time.That is, if no data is transmitted in SFs carrying DRSs, there may beOFDM symbols carrying no physical signal. During operation in anunlicensed band, other nodes may sense a corresponding channel as idleduring this silent interval between DRS transmissions. To avert thisproblem, it is preferable to ensure configuration of transmission burstsincluding DRSs with adjacent OFDM symbols carrying a few signals.

3.5 Channel Access Procedure and Contention Window Adjustment Procedure

Hereinbelow, the afore-described Channel Access Procedure (CAP) andContention Window Adjustment (CWA) will be described from the viewpointof a transmission node.

FIG. 27 is a view illustrating the CAP and CWA.

For a DL transmission, an LTE transmission node (e.g., an eNB) mayinitiate the CAP to operate in unlicensed cell(s), LAA SCell(s) (S2710).

The eNB may select a random backoff count N from a CW. Herein, N is setto an initial value Ninit (S2720).

The eNB determines whether a channel of LAA SCell(s) is idle, and if thechannel is idle, decreases the backoff count by 1 (S2730 and S2740).

In FIG. 27, the order of steps S2730 and S2740 may be changed. Forexample, the eNB may first decrease the backoff count N and thendetermine whether the channel is idle.

If the channel is not idle, that is, the channel is busy in step S2730,the eNB may determine whether the channel is idle during a defer period(equal to or longer than 25 μsec) longer than a slot duration (e.g., 9μsec). If the channel is idle during the defer period, the eNB mayperform the CAP again. For example, if the backoff count Ninit is 10 andafter the backoff count is decreased to 5, the eNB determines that thechannel is busy, the eNB determines whether the channel is idle bysensing the channel during the defer period. If the channel is idleduring the defer period, the eNB may perform the CAP again, starting thebackoff count from 5 (or from 4 after the backoff count is decreased by1), instead of setting the backoff count Ninit.

Referring to FIG. 27 again, the eNB may determine whether the backoffcount N is 0 (S2750). If the backoff count N is 0, the eNB may end theCAP process and transmit a Tx burst including a PDSCH (S2760).

The eNB may receive HARQ-ACK information for the Tx burst from a UE(S2770).

The eNB may adjust a CWS based on the received HARQ-ACK information(S2780).

In step S2780, the CWS may be adjusted in any of the methods describedin Section 4.1.1 to Section 4.1.3 For example, the eNB may adjust theCWS based on HARQ-ACK information for the first SF (i.e., the startingSF) of the latest transmitted Tx burst.

Herein, before performing CWP, the eNB may set an initial CW for eachpriority class. Subsequently, if the probability of determining HARQ-ACKvalues for a PDSCH transmitted in a reference SF to be NACK is at least80%, the eNB increases the CW value set for each priority class to anallowed next level.

In step S2760, the PDSCH may be allocated by SCS or CCS. If the PDSCH isallocated by SCS, the eNB counts the DTX, NACK/DTX, or ANY stateindicated by feedback HARQ-ACK information as NACK. If the PDSCH isallocated by CCS, the eNB counts the NACK/DTX and ANY states indicatedby feedback HARQ-ACK information as NACK meanwhile the eNB does notcount the DTX state indicated by feedback HARQ-ACK information as NACK.

If M (M>=2) SFs are bundled and bundled HARQ-ACK information isreceived, the eNB may regard the bundled HARQ-ACK information as MHARQ-ACK responses. Preferably, the bundled M SFs include a referenceSF.

4. Method for Configuring and Transmitting/Receiving DRS in LAA System

Now, a detailed description will be given of methods for configuring aDRS including a Synchronization Signal (SS) and a Reference Signal (RS)in an unlicensed band, and methods for transmitting and receiving a DRS.In embodiments of the present disclosure, the DRS may be referred to asa discovery signal.

In the LTE-A system, the DRS was designed for RRM measurement for asmall cell which has been deactivated due to an absence of traffic. TheDRS may be configured to be transmitted periodically, once in a unittime of dozens of ms (e.g., 40, 80, or 160 ms). The eNB may configure aDMTC of 6 ms periodically. A UE may receive the DRS within acorresponding DMTC, and use the received DRS in coarse synchronizationacquisition, cell identification, RRM measurement, and so on.

In an LTE system operating in an unlicensed band (i.e., an LAA system),the DRS may include a Primary Synchronization Signal (PSS)/SecondarySynchronization Signal (SSS), and a Cell-specific Reference Signal(CRS). Selectively, the DRS may include a PSS/SSS, a CRS, and a ChannelStatus Information Reference Signal (CSI-RS). As in the LTE-A system,the DRS may be used for acquisition of coarse synchronization, cellidentification, and RRM measurement in the LAA system.

However, the DRS of the LAA system may differ from the DRS of the LTE-Asystem in that an LBT operation may be required for a DRS transmissionin view of the nature of an unlicensed band. For example, if an eNBdiscovers that a channel is occupied by another transmission during anLBT operation for a DRS transmission, the eNB may drop the DRStransmission or attempt the DRS transmission again at another time pointwithin a DMTC period.

FIG. 28 is a view illustrating a DRS transmission method in the LAAsystem.

In the LAA system, the DRS may be transmitted in the following twomethods.

(1) First DRS Transmission Method

Referring to FIG. 28(a), only one time point available for a DRStransmission may be configured within a DMTC period. Therefore, if theeNB fails to transmit the DRS at a DRS transmission time due to an LBTfailure or the like, the eNB drops the DRS transmission.

(2) Second DRS Transmission Method

Referring to FIG. 28(b), a plurality of time points (e.g., every SFboundary) available for a DRS transmission may be configured within aDMTC period. Therefore, even though the eNB fails in LBT, the eNB maytransmit the DRS by performing LBT at another one of the plurality oftime points.

On the other hand, if the DRS is not transmitted during one DMTC perioddue to LBT failure, a UE should wait tens of ms until the next DMTCperiod. In consideration of this characteristic of a DRS transmission,it is preferred that LBT for a DRS without DL data (e.g., a PDSCH) has alarger channel occupancy probability than LBT for DL data.

For example, once the eNB determines that a channel is idle only duringa specific sensing interval, that is, without random backoff,transmission of a DL TX burst including the DRS may be allowed. Herein,a DL TX burst refers to a continuous signal transmission unit. Further,if the eNB determines that the channel is idle only during one of aplurality of sensing intervals divided from a total sensing period, theeNB may allow transmission of a DL TX burst including the DRS.

Referring to FIG. 28(a), it is assumed that the eNB is to transmit theDRS in SF #N and a total sensing period includes three sensingintervals. Even though the channel is busy in the first sensinginterval, the eNB may transmit the DRS because the channel is idle inthe second sensing interval. However, since LBT is completed before thestarting boundary of SF #N, the eNB may transmit a reservation signalduring the remaining interval.

Referring to FIG. 28(b), if the eNB determines that the channel is busyduring the total sensing period shortly before the start of SF #N, theeNB may perform LBT (or CCA) again shortly before the start of the nextSF, SF #N+1. Because the channel is idle in the second sensing intervalas illustrated in FIG. 28(b), the eNB may transmit a reservation signalin the third sensing interval and then transmit the DRS in SF #N+1.

FIG. 29 is a view illustrating an exemplary DRS transmission pattern.

In FIG. 29, it is assumed that the DRS includes a PSS/SSS/CRS. If it isassumed that the DRS includes only a PSS/SSS/CRS without DL data asillustrated in FIG. 29, OFDM symbols including no signal may exist in aperiod to which the DRS is allocated. In FIG. 29, the DRS for the LAAsystem may be transmitted in a 12-OFDM symbol period of one SF, and twoOFDM symbols before or after the SF may be empty. In embodiments of thepresent disclosure, the DRS may be transmitted in one or more DRSoccasions within a DMTC period. One DRS occasion may span a 12-OFDMsymbol period of one SF configured in the UCell.

If LBT is to be performed for signal transmission in the unlicensedband, the eNB may have to perform LBT for CRS transmission in a symbolwith index 0, sym0, and then perform LBT again for CRS transmission insym4. In other words, even though the eNB succeeds in LBT for sym0 inthe unlicensed band and thus transmits a CRS in sym0, the eNB may notmake sure to succeed in LBT for a PSS/SSS/CRS transmission starting insym4.

To prevent this inefficient DRS transmission, an SF carrying the DRS ispreferably transmitted continuously without any empty OFDM symbol. Thesimplest method is that the eNB transmits a dummy signal in empty OFDMsymbols (e.g., sym1, sym2, sym3, sym8, . . . ). However, simpletransmission of the dummy signal leads to waste of radio resources. Inthis context, it is preferable to configure a DRS SF in a more efficientmethod.

While it is assumed that the DRS includes only a PSS/SSS/CRS inembodiments of the present disclosure as described below, for theconvenience of description, the DRS may be configured to selectivelyinclude a CSI-RS, like the legacy DRS.

4.1 Method for Configuring DRS Transmission Pattern

Hereinbelow, a description will be given of a transmission patternsuitable for a DRS transmission in consideration of the afore-describedfirst and second DRS transmission methods and LBT operations.

FIG. 30 is a view illustrating DRS transmission patterns applicable tothe LAA system.

In frame structure 2 (i.e., TDD) of the legacy LTE/LTE-A system, the SSSmay be allocated to the last OFDM symbol of an SF with index 0 or 5(i.e., SF #0 or SF #5), and the PSS may be allocated to the third OFDMsymbol of an SF with index 1 or 6 (i.e., SF #1 or SF #6).

In the embodiments described below (particularly, FIGS. 30 to 32), asolid line represents actual allocation of a PSS/SSS/CRS included in aDRS, and a dotted line represents a candidate position available forallocation of a CRS or the like.

4.1.1 DRS Transmission Pattern for TDD Frame Structure

FIG. 30(a) is a view illustrating a DRS transmission pattern in a TDDframe structure. In FIG. 30(a), transmission of the SSS may not belimited to SF #0 or SF #5, and transmission of the PSS may not belimited to SF #1 or SF #6. For example, it is assumed that the SSS maybe transmitted in any SF, SF #N, and the PSS may be transmitted in SF#N+1.

It is assumed that the DRS includes at least the PSS/SSS/CRS. In thiscase, as illustrated in FIG. 30(a), the DRS may be configured to includeat least an SSS in sym13 of SF #N, a CRS in sym0 of SF #N+1, and a PSSin sym2 of SF #N+1.

The DRS may be configured to include an additional CRS in considerationof a minimum number of OFDM symbols for the CRSs or DRS transmissionLBT. For example, to enable a UE to perform RRM measurement or detect aDRS transmission occasion, it may be assumed that CRSs should betransmitted in at least four OFDM symbols, and a fixed transmissionposition for the DRS is sym11 of SF #N in the first DRS transmissionmethod.

In this case, the eNB may perform LBT during a total sensing periodshortly before sym11 of SF #N. If the eNB succeeds in the LBT, the eNBmay configure the DRS to include a CRS allocated to sym4 of SF #N+1 anda CRS allocated to sym7 of SF #N+1 as well as a CRS allocated to sym11of SF #N.

In another example, on the assumption that CRSs for the DRS istransmitted in at least three OFDM symbols, and a DRS transmission isallowed in sym7 and sym11 of SF #N in the second DRS transmissionmethod, if the eNB succeeds in LBT shortly before sym7 of SF #N, the eNBmay configure the DRS by allocating CRSs to sym7 and sym11 of SF #N. Or,if the eNB succeeds in LBT shortly before sym11 of SF #N, the eNB mayconfigure the DRS to include a CRS allocated to sym4 of SF #N+1 as wellas a CRS allocated to sym11 of SF #N.

In the case of the DRS transmission pattern described with reference toFIG. 30(a), minimum OFDM symbols required for configuring the DRS areacross two or more SFs. Therefore, a PDSCH transmission may beimpossible during two SFs at maximum. If at least one OFDM symbol isneeded for AGC setting before SSS reception, the CRS allocated to sym11of SF #N or a signal allocated to sym10 of SF #N may also be essentialto DRS configuration.

4.1.2 DRS Transmission Pattern for FDD Frame Structure

In frame structure 1 (i.e., FDD structure) of the legacy LTE system, theSSS may be allocated to the sixth OFDM symbol of SF #0 or SF #5, and thePSS may be positioned in the seventh OFDM symbol of SF #0 or SF #5.

In FIG. 30(b), transmission of the PSS/SSS may not be limited to SF #0or SF #5. For example, it is assumed that the PSS/SSS may be transmittedin any SF, SF #N.

It is assumed that the DRS includes at least the PSS/SSS/CRS. In thiscase, as illustrated in FIG. 30(b), the DRS may be configured to includeat least an SSS in sym5 of SF #N, a PSS in sym6 of SF #N, and CRSs insym4 and sym7 of SF #N (or only the CRS in sym4 of SF #N).

The eNB may add a CRS to the DRS configuration illustrated in FIG.30(b), in consideration of a minimum number of OFDM symbols for CRSsrequired for configuring the DRS, or LBT for DRS transmission.

For example, it is assumed that at least three OFDM symbols for CRSs arerequired to configure the DRS, and a fixed transmission position for theDRS is sym0 of SF #N in the first DRS transmission method. Herein, theeNB may perform LBT during a total sensing period shortly before sym0 ofSF #N. If the eNB succeeds in the LBT, the eNB may configure the DRS byallocating a CRS to sym0 of SF #N.

In another example, it is assumed that CRSs are allocated to at leastthree OFDM symbols in order to configure the DRS, and a DRS transmissionis allowed in sym0 or sym4 in the second DRS transmission method.Herein, if the eNB succeeds in LBT shortly before sym0 of SF #N, the eNBmay configure the DRS by allocating a CRS to sym0 of SF #N, and if theeNB succeeds in LBT shortly before sym4 of SF #N, the eNB may configurethe DRS by including a CRS in sym11 of SF #N.

Compared to the DRS transmission pattern described in section 4.1.1,this DRS transmission pattern is advantageous in that a minimum numberof OFDM symbols required for configuring the DRS may form one SF.

4.1.3 DRS Transmission Pattern for TDD and FDD Methods in Combination

The following embodiment is a combination of the embodiments describedin section 4.1.1 and section 4.1.2, and will be described with referenceto FIG. 30(c).

Referring to FIG. 30(c), the eNB may be configured to prepare two OFDMsymbol sets for configuring the DRS, and select one of the OFDM symbolsets according to a situation. More specifically, the eNB may select oneof the two DRS symbol sets according to a position at which LBT for DRStransmission is successful.

For example, it is assumed that a fixed position for a DRS transmissionin SCell #1 is sym0 of SF #N and a fixed position for a DRS transmissionin SCell #2 is sym11 of SF #N in the first DRS transmission method. TheeNB, which has succeeded in LBT shortly before sym0 of SF #N, maytransmit the DRS in SCell #1 in the manner described in section 4.1.2,and the eNB, which has succeeded in LBT shortly before sym11 of SF #N,may transmit the DRS in SCell #2 in the manner described in section4.1.1.

In another example, it is assumed that an OFDM symbol for a DRStransmission is sym0 or sym11 in the second DRS transmission method. Ifthe eNB succeeds in LBT shortly before sym0 of SF #N, the eNB maytransmit the DRS in the manner described in section 4.1.2, and if theeNB succeeds in LBT shortly before sym11 of SF #N, the eNB may transmitthe DRS in the manner described in section 4.1.1.

FIG. 31 is another view illustrating DRS transmission patternsapplicable to the LAA system.

The allocation positions of the PSS/SSS may not be limited to thepositions defined in the LTE-A system. For example, as illustrated inFIG. 31, the PSS/SSS may be at the same positions repeatedly in SFs.Herein, the eNB may determine a PSS/SSS/CRS to be actually transmittedaccording to a position at which LBT for a DRS transmission issuccessful. For example, it is assumed that a DRS transmission isallowed in sym4 or sym11 in the second DRS transmission method. Herein,if the eNB succeeds in LBT shortly before sym4 of SF #N, the eNB maytransmit the DRS in the manner described in section 4.1.2. If the eNBsucceeds in LBT shortly before sym11 of SF #N, the eNB may transmit theDRS in the first DRS transmission method.

This method is advantageous in that since various DRS starting positionsare available, compared to the methods described in section 4.1.1 andsection 4.1.2, a DRS transmission probability may be increased.

4.1.4 DRS Transmission Pattern with No Regard to PSS/SSS Positions ofLTE System

4.1.4.1 Setting of PSS/SSS Positions not Overlapped with CRS Positions

FIG. 32 is a view illustrating another exemplary DRS transmissionpattern applicable to the LAA system.

FIG. 32 is based on the assumption that when the DRS is configured in SF#N, the PSS/SSS forms one set. In the LAA system, the PSS/SSS may beconfigured in OFDM symbols which are not overlapped with the positionsof CRS ports 0, 1, 2 and 3, as illustrated in FIG. 32.

In FIG. 32, the eNB may be configured to transmit the PSS/SSS only insome set(s). Further, the PSS and the SSS may be exchanged in positionin a part or all of configured set(s). Further, a part or all ofconfigured set(s) may include only the SSS or the PSS.

If CRS port 2/3 is not used, the PSS and/or SSS may also be transmittedin an OFDM symbol transmitted through CRS port 2/3. For example, the PSSmay be additionally transmitted in sym1, and the SSS may be additionallytransmitted in sym8.

In FIG. 32, if only transmission of set 1 and set 3 is allowed, the eNBis able to transmit a DRS including set 1 or set 3, and a CRS accordingto the result of DRS LBT. That is, if the eNB succeeds in LBT for DRStransmission shortly before sym0 of SF #N and three CRSs are requiredfor a DRS, the eNB may configure a DRS with CRSs in sym0, sym4, and sym7of SF #N and the PSS/SSS of set 1, and transmit the configured DRS.

Methods for configuring PSS/SSS set(s) in FIG. 32 are given as follows.

(1) PSS/SSS (set 1), SSS/PSS (set 2), [PSS/SSS (set3)]

(2) PSS/SSS (set 1), SSS/PSS (set 2), [SSS/PSS (set3)]

(3) PSS/PSS (set 1), SSS/PSS (set 2), SSS/SSS (set3)

(4) SSS/SSS (set 1), SSS/PSS (set 2), PSS/PSS (set3)

(5) PSS/PSS (set 1), PSS/SSS (set 2), [SSS/SSS (set3)]

Other configurations than the above examples may also possible. However,considering that the PSS may be time-processed with priority over theSSS, a design in which the PSS precedes the SSS may be preferred.Further, if the PSS and the SSS use different numbers of OFDM symbols,the repetition number of the PSS may be set to be larger than that ofthe SSS, considering that the PSS is first processed. Further thePSS/SSS may be configured in a different manner according to an SFnumber.

4.1.4.2 Method for Setting PSS/SSS Positions which May Overlap with CRSPositions

FIG. 33 is a view illustrating a method for configuring a DRStransmission pattern irrespective of CRS positions, which may be appliedto the LAA system.

In embodiments of the present disclosure, PSS/SSS positions may be setwithout considering CRS allocation positions configured by the LTE-Asystem. Herein, as illustrated in FIG. 33, CRSs may be punctured in REsin which the CRSs are overlapped with the PSS/SSS in some OFDM symbols.

That is, the PSS, SSS, and CRS of the DRS may be configured in the sameOFDM symbols, instead of different OFDM symbols.

As described in section 4.1.4.1 and section 4.1.4.2, if an additionalPSS/SSS transmission other than a default PSS/SSS configuration which isalso applied outside a DMTC period or a preset default PSS/SSSconfiguration is allowed, the eNB may indicate a method for configuringan additionally transmitted PSS/SSS to a UE by higher-layer signaling(e.g., RRC signaling).

For example, a method for configuring a PSS/SSS per PSS/SSS set andinformation indicating whether to additionally transmit CRS port 2/3 maybe configurable in section 4.1.4.1. If the SSS/PSS configuration of set2 is a default PSS/SSS configuration, the eNB may indicate the presenceor absence of set 1 and set 3 to a UE in a 2-bit indicator by an RRCsignal. For example, if the 2-bit indicator is set to ‘00’, this mayindicate the absence of PSS/SSS set 1 and PSS/SSS set 3. If the 2-bitindicator is set to ‘01’, this may indicate only the presence of PSS/SSSset 3. If the 2-bit indicator is set to ‘10’, this may indicate only thepresence of PSS/SSS set 1.

Herein, a PSS/SSS set other than set 2 (a default PSS/SSS configurationwhich is also applied outside a DMTC period or a predefined defaultPSS/SSS configuration), and an additional PSS/SSS transmission in OFDMsymbols allocated to CRS port 2/3 may be valid only within a configuredDMTC period.

Further, an additional PSS/SSS other than the default PSS/SSSconfiguration may be configured to be applied only to an SF except forSF #0 or SF #5 within a DMTC period. If multiplexing a DRS with a PDSCHis allowed only in SF #0 and/or SF #5, a UE may advantageously receivethe DRS and/or DL data, assuming the same PDSCH rate matchingirrespective of within or outside the DMTC period.

If it is necessary to indicate that a PSS/SSS in a corresponding SF isdifferent from a default PSS/SSS, the eNB may indicate the difference toa UE for which the SF is scheduled, by DCI. For example, if a PSS/SSSdifferent from a default PSS/SSS is transmitted in SF #0 of a DMTCperiod configured for UE1, and UE2 attempts to receive a PDSCH in SF #0,the eNB may indicate that the PSS/SSS is different from the defaultPSS/SSS for PDSCH rate matching of UE2, by a scheduling grant.

If a PSS/SSS is allowed to be additionally transmitted at a positionother than the legacy allocation positions of the PSS/SSS as in theembodiments described in section 4.1.4.1 and section 4.1.4.2, CSI-RSpositions and PSS/SSS allocation positions may overlap.

To avert this problem, it may be regulated that no CSI-RS is transmittedin or allocated to an SF carrying the PSS/SSS.

Or it may be configured that only the PSS/SSS is transmitted without anyCSI-RS only in an SF in which the CSI-RS collides with the PSS/SSS. Orwhen the CSI-RS collides with the PSS/SSS, the eNB may still transmitthe remaining CSI-RS ports, while dropping only the collided CSI-RSports.

Or the eNB may allocate a CSI-RS in a manner that prevents collisionbetween the CSI-RS and the PSS/SSS.

Before receiving the DRS, the UE may need at least one OFDM symbol, forAGC setting. For this purpose, transmission of the CRS, PSS, and SSS (orother signals such as the CSI-RS) may start one OFDM symbol before theDRS transmissions described in section 4.1.1 to section 4.1.4, and thecorresponding OFDM symbol may be used only for the usage of AGC setting.

4.2 Method for Configuring Subframe Numbers for DRS Transmission

Now, a description will be given of methods for configuring SF numbers,if the SF numbers of SFs carrying the PSS/SSS/CRS for DRS transmissionare different from those in the LTE/LTE-A system in the afore-describedsection 4.1.1 to section 4.1.3.

FIG. 34 is a view illustrating methods for configuring an SF number forDRS transmission applicable to the LAA system.

Since the SSS is always transmitted in SF #0 and SF #5 in TDD and FDDsystems, the following description is given in the context of the SSS,for the convenience of description. However, the corresponding methodsare also applicable in the same manner to the case where the PSS, CRS,and/or CSI-RS is generated. Further, it is assumed in FIG. 34 that thesame SF numbers are configured for a PCell of a licensed band and aUCell (i.e., SCell) of an unlicensed band. However, in the state whereSF boundaries are synchronized between the PCell and the UCell,different SF numbers may be set on a cell basis.

In FIG. 34, the top drawing illustrates the SF numbers of a PCell on aframe basis. For example, SF #0 to SF #9 included in each of SF #N andSF #N+1 are shown. Further, the other drawings are intended to describeSF numbers reconfigured in a serving cell of the LAA system, a UCell.

4.2.1 SF Number Reconfiguration Method 1

Referring to FIG. 34(a), if an SSS is transmitted in the UCell in SF #3of the PCell, the eNB reconfigures the SF number of the UCell as SF #0and maintains the reconfigured SF number (as far as the SSS iscontinuously transmitted in SF #0 or SF #5).

For example, a sequence such as a CRS and/or a CSI-RS transmitted ineach SF is generated based on the reconfigured SF number. However, if aUE fails to receive the SSS of the UCell, transmitted in SF #3 of thePCell, the UE fails to receive a CRS and a CSI-RS in a subsequent SF,thereby degrading DL data reception performance.

4.2.2 SF Number Reconfiguration Method 2

Referring to FIG. 34(b), if the SSS of the UCell is transmitted in SF #3of the PCell, the eNB may reconfigure the SF number of the correspondingSF as SF #0, and maintain the reconfigured SF number only within oneradio frame.

More specifically, a sequence such as a CRS/CSI-RS transmitted in eachSF is generated based on the reconfigured SF number. Compared to theembodiment of section 4.2.1, even though there is a UE which has failedto receive the SSS of the UCell transmitted in SF #3 of the PCell, theUE may have a problem in receiving a DL signal only during one radioframe at maximum, and operate normally from the next radio frame. TheCSI-RS and/or CSI-IM in the DRS and the legacy configured CSI-RS and/orCSI-IM may also be configured based on the reconfigured SF #0, However,for this purpose, the resulting Blind Detection (BD) of the PSS/SSS in awhole DMTC period may increase the complexity of UE implementation.

4.2.3 SF Number Reconfiguration Method 3

Referring to FIG. 34(c), an SF number may not be changed irrespective ofan SF in which the SSS of the UCell is transmitted. Specifically, asequence such as a CRS/CSI-RS transmitted in each SF is generated basedon an SF number (a predetermined SF number) of the PCell irrespective ofthe transmission positions of the PSS/SSS. In the LTE-A system, an SSSincluded in a DRS may be configured as a different sequence, dependingon whether the SSS is transmitted in SF #0 or SF #5.

If the SSS is transmitted in an SF other than SF #0 or SF #5 in theforegoing embodiments, a sequence which is used for configuring asynchronization signal in SF #0 or SF #5 (or a modification to thesequence) is configured to be applied for transmitting the SSS.

Or it may be configured that SSSs of SF #0 to SF #4 may be generated andtransmitted based on a sequence (or a modification to the sequence)transmitted in SF #0, and SSSs of SF #5 to SF #9 may be generated andtransmitted based on a sequence (or a modification to the sequence)transmitted in SF #5. For example, if SSSs are transmitted in SF #0 toSF #4 of the UCell, a first sequence may be used to generate the SSSs inSF #0 to SF #4. Further, if SSSs are transmitted in SF #5 to SF #9 ofthe UCell, a second sequence may be used to generate the SSSs in SF #5to SF #9. The first sequence refers to a sequence used to generate anSSS in SF #0 of the PCell, SCell or UCell, and the second sequencerefers to a sequence used to generate an SSS in SF #5 of the PCell,SCell or UCell.

However, if the legacy PSS/SSS is not transmitted every 5 ms to a UEwhich is to perform cell detection in the SCell, the UE may fail in thecell detection. Accordingly, only when the SF number of an SF carryingthe PSS/SSS is different between the LAA system and the LTE-A system,the PSS/SSS of the LAA system needs to be transmitted differently fromthe PSS/SSS of the LTE-A system.

For example, when the eNB transmits the PSS/SSS, the eNB may usefrequency resources other than six center PRBs in a system bandwidth.This is because considering that the bandwidth of an LTE systemoperating in an unlicensed band may be at least 5 MHz, there is no needfor limiting the PSS/SSS to the six center PRBs.

Further, frequency resources may be preset according to the SF number ofan SF carrying the PSS and/or the SSS actually.

Or, the eNB may be configured to transmit the PSS and/or the SSS in adifferent frequency for each cell through inter-cell coordination inconsideration of inter-cell interference in the same frequency band.

4.2.4 SF Number Reconfiguration Method 4

The eNB may reconfigure the SF number of an SF carrying the SSS in theUCell as SF #0, and apply the reconfigured SF number only within a DRSoccasion.

FIG. 34(d) illustrates an SF structure in the case where a DRS occasionis two SFs in DMTC1 and three SFs in DMTC2. The sequence of anSSS/CRS/CSI-RS transmitted in a DRS occasion starting from an SFcarrying the SSS in DMTC1 and DMTC2 is generated based on a reconfiguredSF number in the UCell, irrespective of an SF number in the PCell.

4.2.5 SF Number Reconfiguration Method 5

The eNB may reconfigure the SF number of an SF carrying the SSS in theUCell as SF #0 or SF #5, and apply the reconfigured SF number onlywithin a DRS occasion. Herein, if the DRS occasion includes SF #0 to SF#4 of the PCell, the SF number of an SF carrying the SSS of the UCellmay be configured as SF #0, and if the DRS occasion includes SF #5 to SF#9 of the PCell, the SF number of an SF carrying the SSS of the UCellmay be configured as SF #5.

FIG. 34(e) illustrates an example in which a DRS occasion spans two SFsin DMTC1 and three SFs in DMTC2. The sequence of an SSS/CRS/CSI-RStransmitted in a DRS occasion starting from an SF carrying the SSS inDMTC1 and DMTC2 is generated based on a reconfigured SF number in theUCell irrespective of an SF number in the PCell.

For example, referring to FIG. 34(e), SF #3 of the UCell correspondingto SF #3 of the PCell in DMTC1 is a DRS occasion, and an SSS included ina DRS may be transmitted in SF #3 of the UCell. Herein, SF #3 of theUCell is reconfigured as SF #0, and SF #3 and SF #4 of the UCell arereconfigured as SF #0 and SF #1 in the DRS occasion. Further, SF #7 ofthe UCell corresponding to SF #7 of the PCell in DMTC2 may be a DRSoccasion. Thus, SF #7 to SF #9 of the UCell are reconfigured as SF #5 toSF #7. In this case, a PSS/SSS/CRS included in a DRS transmitted inDMTC1 and DMTC2 may be generated based on a reconfigured SF number inthe UCell.

4.2.6 SF Number Reconfiguration Method 6

The eNB may reconfigure the SF number of an SF carrying the SSS in theUCell as SF #0, and maintain the reconfigured SF number in a DRSoccasion.

FIG. 34(f) illustrates an example in which a DRS occasion spans two SFsin DMTC1 and three SFs in DMTC2. The sequence of an SSS/CRS/CSI-RStransmitted in a DRS occasion starting from an SF carrying the SSS inDMTC1 and DMTC2 is generated based on a reconfigured SF number in theUCell irrespective of an SF number in the PCell.

4.2.7 SF Number Reconfiguration Method 7

The eNB may reconfigure the SF number of an SF carrying the SSS in theUCell as SF #0 or SF #5, and maintain the reconfigured SF number in aDRS occasion. If a DRS occasion is SF #0 to SF #4 of the PCell, SFnumbers in the DRS occasion starting from an SF carrying the SSS in theUCell may be reconfigured as SF #0. Further, if a DRS occasion is SF #5to SF #9 of the PCell, SF numbers in the DRS occasion starting from anSF carrying the SSS in the UCell may be reconfigured as SF #5.

FIG. 34(g) illustrates an example in which a DRS occasion spans two SFsin DMTC1 and three SFs in DMTC2. The sequence of an SSS/CRS/CSI-RStransmitted in a DRS occasion starting from an SF carrying the SSS inDMTC1 and DMTC2 is generated based on a reconfigured SF number in theUCell irrespective of an SF number in the PCell.

4.2.8 SF Number Reconfiguration Method 8

If the SF number of an SF carrying the SSS in the UCell is SF #0 of thePCell, the eNB may reconfigure the SF number as SF #0, and if the SFnumber of the SF carrying the SSS in the UCell is SF #5 of the PCell,the eNB may reconfigure the SF number as SF #5.

If a DRS occasion corresponds to SF #0 to SF #4 of the PCell, the eNBmay reconfigure SF numbers in a DRS occasion starting from an SFcarrying the SSS in the UCell as SF #A (e.g., A=1). In addition, if aDRS occasion corresponds to SF #6 to SF #9 of the PCell, the eNB mayreconfigure SF numbers in a DRS occasion starting from an SF carryingthe SSS in the UCell as SF #13 (e.g., B=6 or the same value as A).

FIG. 34(h) illustrates an example in which a DRS occasion spans two SFsin DMTC1 and three SFs in DMTC2. Or in FIG. 34(h), both the DRSoccasions in DMTC1 and DMTC2 may be configured to be commonly one SF.

The eNB may generate a sequence with which to generate an SSS/CRS/CSI-RStransmitted in a DRS occasion starting from an SF carrying the SSS inDMTC1 and DMTC2 based on a reconfigured SF number irrespective of an SFnumber in the PCell.

4.2.9 SF Number Reconfiguration Method 9

The eNB may configure an SF number of the UCell irrespective of an SFnumber of the PCell in a DMTC period irrespective of a DRS occasion. Forexample, a sequence with which to generate an SSS/CRS/CSI-RS within aDMTC period may be generated on the assumption of SF #X (e.g., X=0).

Or if SF indexes within a DMTC period are SF #0 to SF #4, a sequencewith which to generate an SSS/CRS/CSI-RS may be generated on theassumption of SF #Y (e.g., Y=0). Further, if SF indexes within a DMTCperiod are SF #5 to SF #9, a sequence with which to generate anSSS/CRS/CSI-RS may be generated on the assumption of SF #Z (e.g., Z=5).

Among the methods for reconfiguring an SF number of a UCell andgenerating the sequence of an SSS/CRS/CSI-RS based on the reconfiguredSF as proposed by the afore-described section 4.2.1 to section 4.2.9,different methods may be applied to the cases of SSS, CRS, and CSI-RS.For example, the sequences of an SSS and a CSI-RS may generatedaccording to the embodiment described in section 4.1.5, whereas thesequence of a CRS may generated according to the embodiment described insection 4.1.3.

4.3 DRS Configuration Method

In embodiments of the present disclosure, empty OFDM symbols may beincluded in a DRS transmission period (e.g., a DRS occasion). A dummysignal may be transmitted or a CSI-RS may be allocated and transmitted,in the empty OFDM symbols. Further, a CRS may be allowed to betransmitted at a position which has not been defined in the L E-Asystem.

Even in this case, the above-described embodiments may be extended. Forexample, referring to section 4.1.2 and FIG. 30(b), it may be configuredthat a CRS is also transmitted in sym2 to increase the RRM measurementperformance of a UE in an unlicensed band. In this case, if at leastfour OFDM symbols are needed for CRSs and sym0 of SF #n is a fixedposition in the first DRS transmission method, the eNB performs LBTduring a total sensing period shortly before sym0 of SF #N. If the LBTis successful, the eNB may configure a DRS to include CRSs in sym0 andsym2 of SF #N.

If empty OFDM symbols are filled with CSI-RSs and/or CRSs in a DRSoccasion, whether the CSI-RSs or CRSs may be used for a UE in cellidentification, CSI measurement, or RRM measurement may be an issue.That is, the following two options may be available depending on whetherempty OFDM symbols are utilized.

4.3.1 Option 1

From the viewpoint of the eNB, when a PDSCH and a DRS are multiplexed ina DRS transmission SF, the eNB may not fill an empty OFDM symbol with anadditional RS (e.g., CRS/CSI-RS). However, the eNB may fill an emptyOFDM symbol with a predefined CSI-RS and/or CRS in an SF carrying theDRS which is not multiplexed with the PDSCH. That is, in the case wherethe DRS is multiplexed with the PDSCH, no empty OFDM symbol isgenerated. Thus, the eNB does not need for adding a CSI-RS/CRS. On thecontrary, in the case where the DRS is not multiplexed with the PDSCH,an empty OFDM symbol is generated. Thus, the eNB may additionallyallocate a CSI-RS/CRS to the empty OFDM symbol.

From the viewpoint of a UE, if the UE receives a DRS in a configuredDMTC period, the UE may assume that there is no additional CSI-RS or CRStransmitted in an empty OFDM symbol irrespective of whether the UE isscheduled for a corresponding SF. For example, even though a DRS and aPDSCH are multiplexed in a corresponding SF, a UE scheduled for the SFwithin a configured DMTC period does not perform rate matching on anadditional CSI-RS and/or CRS in an empty OFDM symbol that does not carrythe DRS.

In another example, a UE, which has received only a DRS (not a PDSCH)within a configured DMTC period, may basically assume no additionalCSI-RS and/or CRS in an empty OFDM symbol. However, only in the casewhere the UE is capable of determining whether there is an additionalCSI-RS and/or CRS transmittable in an empty OFDM symbol by BD, if the UEdetects the additional CSI-RS and/or CRS, the UE may use the detectedCSI-RS and/or CRS in cell identification, CSI measurement, RRMmeasurement, or the like.

4.3.2 Option 2

From the viewpoint of the eNB, if a PDSCH and a DRS are multiplexed in aDRS transmission SF, the eNB may not fill an empty OFDM symbol with anadditional RS. Regarding an SF carrying only a DRS which is notmultiplexed with a PDSCH, the eNB may fill an empty OFDM symbol with apredetermined CSI-RS and/or CRS at least in a predetermined SF (e.g., anSF other than SF #0/#5) and transmit the OFDM symbol.

From the viewpoint of the UE, upon receipt of a DRS within a configuredDMRS period, if the DRS is multiplexed with a PDSCH in a correspondingSF, the UE does not perform rate matching on an additional CSI-RS and/orCRS in an empty OFDM symbol in which the DRS is not transmitted.

On the other hand, if the UE receives only a DRS (not a PDSCH) within aconfigured DMTC period, the UE may use an additional CSI-RS and/or CRSin cell identification, CSI measurement, RRM measurement, or the like,basically assuming that the additional CSI-RS and/or CRS always existsin an empty OFDM symbol at least in a predetermined SF (e.g., an SFother than SF #0/#5).

However, only in the case where the UE is capable of determining whetherthere is an additional CSI-RS and/or CRS transmittable in an empty OFDMsymbol by BD, if the UE detects the additional CSI-RS and/or CRS, the UEmay use the detected CSI-RS and/or CRS in cell identification, CSImeasurement, RRM measurement, or the like.

PSS/SSS/CRS transmission patterns configured in the above-describedmethods may not be limited to within a DMTC period. For example, the eNBmay transmit a DRS including a PSS/SSS/CRS (or CSI-RS) for the purposeof time and frequency synchronization of a specific UE to the UE, evenin an SF which is not included in a DMTC period configured for the UE.

Further, the PSS/SSS/CRS transmission patterns configured in theabove-described methods may be applied in the same manner to a DL TXburst including DL data as well as a DL TX burst including only a DRS.Herein, an LBT method for a DL TX burst including only a DRS may beconfigured in the same manner as an LBT method for DRS transmissionwithin a DMTC period.

The sequence generation methods described in section 4.2.1 to section4.2.9 may be applied in the same manner to outside a DMTC periodconfigured for a UE. For example, as in section 4.2.9, an SSS/CRS/CSI-RSmay be generated on the assumption of SF #X (e.g., X=0) in every SF(irrespective of a DMTC period).

Or as described in section 4.2.9, for every SF (irrespective of a DMTCperiod), if SF indexes are SF #0 to SF #4, an SSS/CRS/CSI-RS may begenerated on the assumption of SF #Y (e.g., Y=0), and if SF indexes areSF #5 to SF #9, an SSS/CRS/CSI-RS may be generated on the assumption ofSF #Z (e.g., Z=5).

4.4. Method for Notifying DRS Transmission Time

Methods for notifying a UE of a DRS transmission time in order toincrease the DRS reception probability of the UE will be describedbelow.

The eNB may indicate to a UE by DCI when a DRS transmission actuallystarts within a DMTC period or whether a DRS is transmitted outside theDMTC period. Herein, the eNB may signal whether a DRS is transmitted ornot by common DCI or DCI indicating the presence or absence of aCSI-RS/CSI-IM to the UE.

If the UE misses the DCI, the UE may consider that no DRS has beentransmitted. However, even though the eNB determines that a DRS (i.e.,PSS/SSS/CRS) transmission is enough to satisfy a requirement, the UE maynot satisfy the requirement. Therefore, even though the UE has missedthe DCI, the UE may be configured to attempt DRS reception.

The eNB may transmit a DRS except for some OFDM symbols due to theinfluence of an LBT completion time or the like. Characteristically,even though the DRS is transmitted without some OFDM symbols, minimumOFDM symbols that should be included may be predetermined. For example,it may be regulated that at least a CRS/SSS/PSS/CRS is allocated to andtransmitted in sym4, sym5, sym6, and sym7 in FIG. 30(b).

It is assumed that the eNB has transmitted only a CRS/SSS/PSS/CRSallocated to sym4, sym5, sym6, and sym7 instead of a DRS defined in sym0to sym12, in an SF. Herein, a UE for which the corresponding SFs areconfigured as a DMTC period may have difficulty in determining that avalid DRS has been transmitted in the corresponding SFs. Instead, a UEfor which the corresponding SFs are not configured as a DMTC period mayuse a PSS/SSS/CRS/CSI-RS in the corresponding SFs for time/frequencysynchronization, CSI measurement, RRM measurement, or the like.

The foregoing embodiments are not related to introduction ornon-introduction of a partial TTI. Further, if the eNB transmits areservation signal, an initial signal, or a preamble in sym4 to sym7(particularly SF #0 and SF #5), the eNB may transmit a DRS(PSS/SSS/CRS/CSI-RS). For a UE for which the corresponding SF isconfigured as a DMTC period, a valid DRS is still not received in theconfigured DMTC period. Thus, the eNB may also transmit a DRS (definedin sym0 to sym12) in the next SF, for the UE.

4.5 DRS Reception Method

If the sequence of a CRS/CSI-RS may be determined irrespective of an SFindex in a PCell (i.e., according to an SF number in a UCell) in theabove-described embodiments, a UE may face ambiguity in demodulating an(E)PDCCH/PDSCH or measuring CSI in an SF carrying a DRS. To solve theproblem, the following methods may be considered.

4.5.1 DRS Reception Method 1

The UE may assume a different CRS/CSI-RS sequence in a predeterminedrule, only for SFs in which a PSS and/or an SSS is detected outside aDMTC period configured for the UE.

For example, if a DRS occasion is SF indexes SF #0 to SF #4, the eNB maygenerate a sequence for an SSS/CRS/CSI-RS on the assumption of SF #0, asin the methods described in section 4.2.5. In addition, if a DRSoccasion is SF indexes SF #5 to SF #9, the eNB may generate a sequencefor an SSS/CRS/CSI-RS on the assumption of SF #5. Herein, if the UEdetects a PSS and/or an SSS in an SF, the UE may perform decoding,assuming the sequence of a CRS/CSI-RS according to the sequence of thedetected SSS.

4.5.2 DRS Reception Method 2

Only for an SF indicated preliminarily by RRC signaling or an SFindicated dynamically by a physical-layer signal by the eNB, the UE mayperform decoding, on the assumption of a CRS/CSI-RS sequence of aspecific SF index.

4.5.3 DRS Reception Method 3

This embodiment may be implemented by section 4.5.1 and section 4.5.2 incombination. For example, if the eNB indicates a set of SFs in which aCRS/CSI-RS is transmittable irrespective of an SF index of the PCell,the UE may attempt to detect a PSS and/or an SSS only in the SFs of theset. Once the UE detects the PSS/SSS in the corresponding SFs, the UEmay determine a CRS/CSI-RS sequence in a predetermined rule or byassuming an SF index configured by signaling.

Herein, different operations may be defined for within or outside a DMTCperiod configured for a UE. For example, the UE may receive a DRSincluding a CSI-RS and the like by assuming the same CSI-RS sequence asfor a CSI-RS of the legacy LTE-A (Rel-12) system, within the DMTC periodconfigured for the UE, whereas the UE may apply the embodimentsdescribed in section 4.5.1 to section 4.5.3, outside the DMTC period.

4.6 DRS Transmission Method

FIG. 35 is a view illustrating an exemplary DRS transmission methodapplicable to the LAA system.

The embodiments of the present invention described in section 1 tosection 4 in combination may be applied to the embodiment described withreference to FIG. 35. Referring to FIG. 35, when the eNB needs totransmit a DRS, the eNB determines whether a corresponding channel (orUCell) is idle in a DRS occasion within a DMTC period or shortly beforethe DRS occasion (S3510).

In step S3510, it may be determined whether the channel is idle or notby sensing the channel for a predetermined time or performing LBT at theeNB (refer to section 3).

If the channel is an idle state, the eNB may generate a DRS (S3520) andtransmit the DRS to a UE (S3530).

In step S3520, the DRS is configured to include a PSS, an SSS, and aCRS. Optionally, the DRS may include a CSI-RS. In cases of the PSS, SSS,CRS and CSI-RS are generated, they are generated based on an SF index(or SF number) of the UCell in which the DRS is to be transmitted.

For example, the PSS may be transmitted in the last OFDM symbol of thefirst slot of a DRS occasion, and the SSS may be transmitted in the slotcarrying the PSS. Herein, the DRS occasion may be transmitted in areconfigured SF of the UCell, and section 4.2 may be referred to for themethods for retransmitting an SF.

For example, sequences required to generate SSSs are determined based ona reconfigured SF number of the UCell. More specifically, if the SSSsare transmitted in SF #0 to SF #4 of the UCell, the SSSs are generatedbased on a first sequence used in SF #0. Further, if the SSSs aretransmitted in SF #5 to SF #9 of the UCell, the SSSs are generated basedon a second sequence used in SF #5.

Further, if CRSs are transmitted in SF #0 to SF #4 of the UCell, theCRSs are generated based on a sequence used in SF #0. Further, if theCRSs are transmitted in SF #5 to SF #9 of the UCell, the CRSs aregenerated based on a sequence used in SF #5.

That is, based on a subframe number of the subframe of the UCell where aDRS occasion is occurred, a sequence for the PSS/SSS/CRS/CSI-RS of theDRS may be generated based on a reconfigured SF number of the UCell.

Further, the UE may estimate and determine a sequence used to generatethe PSS, SSS, CRS, and/or CSI-RS of the DRS based on the SF number ofthe SF in which the DRS occasion has occurred.

Referring to FIG. 35 again, the UE may receive DRSs in DRS occasionswithin the DMTC period. The UE may acquire time/frequencysynchronization, measure and report CSI, and measure and report RRMbased on the received DRSs (S3540).

In the embodiments of the present disclosure, SF numbers are expressedas 0 or larger integers.

5. Apparatuses

Apparatuses illustrated in FIG. 36 are means that can implement themethods described before with reference to FIGS. 1 to 35.

A UE may act as a transmission end on a UL and as a reception end on aDL. An eNB may act as a reception end on a UL and as a transmission endon a DL.

That is, each of the UE and the eNB may include a Transmitter (Tx) 3640or 3650 and a Receiver (Rx) 3660 or 3670, for controlling transmissionand reception of information, data, and/or messages, and an antenna 3600or 3610 for transmitting and receiving information, data, and/ormessages.

Each of the UE and the eNB may further include a processor 3620 or 3630for implementing the afore-described embodiments of the presentdisclosure and a memory 3680 or 3690 for temporarily or permanentlystoring operations of the processor 3620 or 3630.

The embodiments of the present disclosure may be implemented by use ofthe components and functions of the afore-described UE and eNB. Forexample, the processor of the eNB may perform CAP (or CS, CAA, or thelike) for determining whether an LAA cell is idle by controlling the Txand Rx. Further, the processor of the eNB may determine whether thechannel is idle in or before DRS occasions. If the channel is idle, theprocessor of the eNB may generate a DRS and transmit the DRS to a UE.For details of the methods for generating a DRS, section 1 to section 4may be referred to.

The Tx and Rx of the UE and the eNB may perform a packetmodulation/demodulation function for data transmission, a high-speedpacket channel coding function, OFDM packet scheduling, TDD packetscheduling, and/or channelization. Each of the UE and the eNB of FIG. 36may further include a low-power Radio Frequency (RF)/IntermediateFrequency (IF) module.

Meanwhile, the UE may be any of a Personal Digital Assistant (PDA), acellular phone, a Personal Communication Service (PCS) phone, a GlobalSystem for Mobile (GSM) phone, a Wideband Code Division Multiple Access(WCDMA) phone, a Mobile Broadband System (MBS) phone, a hand-held PC, alaptop PC, a smart phone, a Multi Mode-Multi Band (MM-MB) terminal, etc.

The smart phone is a terminal taking the advantages of both a mobilephone and a PDA. It incorporates the functions of a PDA, that is,scheduling and data communications such as fax transmission andreception and Internet connection into a mobile phone. The MB-MMterminal refers to a terminal which has a multi-modem chip built thereinand which can operate in any of a mobile Internet system and othermobile communication systems (e.g. CDMA 2000, WCDMA, etc.).

Embodiments of the present disclosure may be achieved by various means,for example, hardware, firmware, software, or a combination thereof.

In a hardware configuration, the methods according to exemplaryembodiments of the present disclosure may be achieved by one or moreApplication Specific Integrated Circuits (ASICs), Digital SignalProcessors (DSPs), Digital Signal Processing Devices (DSPDs),Programmable Logic Devices (PLDs), Field Programmable Gate Arrays(FPGAs), processors, controllers, microcontrollers, microprocessors,etc.

In a firmware or software configuration, the methods according to theembodiments of the present disclosure may be implemented in the form ofa module, a procedure, a function, etc. performing the above-describedfunctions or operations. A software code may be stored in the memory3680 or 3690 and executed by the processor 3620 or 3630. The memory islocated at the interior or exterior of the processor and may transmitand receive data to and from the processor via various known means.

Those skilled in the art will appreciate that the present disclosure maybe carried out in other specific ways than those set forth hereinwithout departing from the idea and essential characteristics of thepresent disclosure. The above embodiments are therefore to be construedin all aspects as illustrative and not restrictive. The scope of thedisclosure should be determined by the appended claims and their legalequivalents, not by the above description, and all changes coming withinthe meaning and equivalency range of the appended claims are intended tobe embraced therein. It is obvious to those skilled in the art thatclaims that are not explicitly cited in each other in the appendedclaims may be presented in combination as an embodiment of the presentdisclosure or included as a new claim by a subsequent amendment afterthe application is filed.

INDUSTRIAL APPLICABILITY

The present disclosure is applicable to various wireless access systemsincluding a 3GPP system, a 3GPP2 system, and/or an IEEE 802.xx system.Besides these wireless access systems, the embodiments of the presentdisclosure are applicable to all technical fields in which the wirelessaccess systems find their applications.

1. A method for transmitting a discovery reference signal (DRS) by abase station in a wireless access system supporting an unlicensed band,the method comprising: configuring the DRS to be transmitted in anunlicensed band cell (UCell) configured in the unlicensed band; andtransmitting the configured DRS in a DRS occasion, wherein the DRSincludes a primary synchronization signal (PSS), a secondarysynchronization signal (SSS), and a cell-specific reference signal(CRS), wherein the SSS is generated based on a subframe (SF) number ofan SF in which the DRS occasion occurs, and wherein if the SF number isSF #0 to SF #4, the SSS is generated based on a sequence correspondingto SF #0, and if the SF number is SF #5 to SF #9, the SSS is generatedbased on a sequence corresponding to SF #5.
 2. The method according toclaim 1, further comprising: performing a channel sensing procedure todetermine whether the UCell is idle, before transmitting the DRS.
 3. Themethod according to claim 1, wherein if the SF number of an SF carryingthe CRS is SF #0 to SF #4, the CRS is generated based on the sequencecorresponding to SF #0, and wherein if the SF number of the SF carryingthe CRS is SF #5 to SF #9, the CRS is generated based on the sequencecorresponding to SF #5.
 4. The method according to claim 1, wherein theDRS is transmitted along with a physical downlink shared channel (PDSCH)only in SF #0 or SF #5.
 5. The method according to claim 1, wherein theDRS is configured to further include a channel statusinformation-reference signal (CSI-RS).
 6. A base station fortransmitting a discovery reference signal (DRS) in a wireless accesssystem supporting an unlicensed band, the base station comprising: atransmitter; and a processor for configuring the DRS, wherein theprocessor is configured to configure the DRS to be transmitted in anunlicensed band cell (UCell) configured in the unlicensed band, and totransmit the configured DRS in a DRS occasion by controlling thetransmitter, wherein the DRS includes a primary synchronization signal(PSS), a secondary synchronization signal (SSS), and a cell-specificreference signal (CRS), wherein the SSS is generated based on a subframe(SF) number of an SF in which the DRS occasion occurs, and wherein ifthe SF number is SF #0 to SF #4, the SSS is generated based on asequence corresponding to SF #0, and if the SF number is SF #5 to SF #9,the SSS is generated based on a sequence corresponding to SF #5.
 7. Thebase station according to claim 6, wherein the processor is configuredfurther to perform a channel sensing procedure to determine whether theUCell is idle, before transmitting the DRS.
 8. The base stationaccording to claim 6, wherein if the SF number of an SF carrying the CRSis SF #0 to SF #4, the CRS is generated based on the sequencecorresponding to SF #0, and wherein if the SF number of the SF carryingthe CRS is SF #5 to SF #9, the CRS is generated based on the sequencecorresponding to SF #5.
 9. The base station according to claim 6,wherein the DRS is transmitted along with a physical downlink sharedchannel (PDSCH) only in SF #0 or SF #5.
 10. The base station accordingto claim 6, wherein the DRS is configured to further include a channelstatus information-reference signal (CSI-RS).